Control system

ABSTRACT

A control system which is capable of compensating for and suppressing the influence of a periodic disturbance on a controlled object more quickly, even when the controlled object is subjected to the periodic disturbance the amplitude of which periodically changes, thereby enhancing the stability and the accuracy of control. The control system includes an ECU. The ECU calculates disturbance compensation values for compensating for a periodic disturbance by searching maps and tables, in timing of generation of each pulse of a CRK signal. The ECU calculates control inputs at a predetermined control period, with predetermined control algorithms, according to the disturbance compensation values read in at the control period, respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a control system that controls a controlledobject to which is applied periodic disturbance the amplitude of whichperiodically changes.

2. Description of the Related Art

Conventionally, a control system that controls a variable cam phasemechanism of an internal combustion engine has been disclosed in PatentLiterature 1 (Japanese Laid-Open Patent Publication (Kokai) No.2001-132482). This variable cam phase mechanism changes the phase of anintake camshaft, i.e. an intake cam, with respect to a crankshaft(hereinafter referred to as “the cam phase”) as desired to therebychange the valve timing of intake valves, and is comprised of ahydraulically-driven variable cam phase mechanism, and a solenoidcontrol valve for supplying hydraulic pressure from an oil pump to thevariable cam phase mechanism. Further, the control system includes acrank angle sensor and a cam angle sensor which output signalsindicative of the angle position of the crankshaft and that of theintake cam, respectively, and a controller to which are inputted thedetection signals from the sensors.

The controller calculates an actual cam phase based on the detectionsignals from the crank angle sensor and the cam angle sensor, and atarget cam phase depending on operating conditions of the engine, and asdescribed hereinafter, controls the variable cam phase mechanism with asliding mode control algorithm such that the cam phase is caused toconverge to the target cam phase. In other words, the controller regardsa system to which is inputted a control signal for the solenoid controlvalve as a control input and from which is outputted the cam phase, as acontrolled object, and models the controlled object into acontinuous-time system model. More specifically, the characteristicequation of the controlled object is set as a differential equation inwhich the first-order and second-order time derivative values of the camphase are represented as state variables. Further, a switching functionof the sliding mode control algorithm is set as a linear function inwhich the difference between the target cam phase and the cam phase anda time derivative value of the difference (i.e. the rate of change inthe difference) are represented as state variables. Then, the controlinput is calculated such that the difference and the rate of change inthe difference set as above as the state variables of the switchingfunction are on a switching line. In other words, the control input iscalculated such that the difference and the rate of change in thedifference slide on the switching line to converge to a value of 0,whereby the cam phase is caused to converge to the target cam phase.

Further, a control system using the sliding mode control algorithm hasbeen proposed in Patent Literature 2 (Japanese Laid-Open PatentPublication (Kokai) No. 2003-5804) by the present assignee. This controlsystem controls a throttle valve-actuating mechanism for the engine, andincludes an adaptive sliding mode controller, an onboard identifier, astate predictor, and so forth. Further, the throttle valve-actuatingmechanism actuates a throttle valve to thereby change the degree ofopening thereof, and includes a motor.

In the control system, a control input for control of the throttlevalve-actuating mechanism is calculated as follows: A system to which isinputted the duty ratio of a control signal supplied to the motor as acontrol input and from which is outputted the difference between thedegree of opening of the throttle valve and a target degree of openingthereof is regarded as a controlled object, and the controlled object ismodeled into a discrete-time system model defining the relationshipsbetween the duty ratio, the difference between the degree of opening ofthe throttle valve and the target degree of opening thereof, and acompensation value. The compensation value is for compensating formodeling errors in modeling the controlled object, and disturbance.

Then, model parameters of the controlled object model and thecompensation value are calculated for identification by the onboardidentifier, and the control input is calculated by the adaptive slidingmode controller, using the above identified values, with the slidingmode control algorithm. In the control system, since the control inputis calculated as above, it is possible to properly compensate for themodeling errors and the disturbance, thereby making it possible toensure high accuracy of control.

The control system proposed in Patent Literature 1 suffers from thefollowing problems: (f1) The influence of disturbance on the controlledobject is not taken into account, and hence when the controlled objectis a variable cam phase mechanism which is liable to be subjected to asteady-state disturbance, the stability and the accuracy of control isdegraded by the steady-state disturbance. (f2) Further, the variable camphase mechanism is provided for changing the phase of the intake camwith respect to the crankshaft, as desired, and hence when the intakecam actuates the intake valve to open and close the same, the intake camis subjected to a periodic disturbance the amplitude of whichperiodically changes, due to the urging force and the reaction force ofa valve spring of the intake valve (see FIG. 12, referred tohereinafter). When such a periodic disturbance is applied to thevariable cam phase mechanism, the total valve open time period of theintake valve is shortened by the influence of the periodic disturbance(see FIGS. 14 and 15, referred to hereinafter), and the amount of intakeair decreases when the intake valve is opened. This reduces torquegenerated by the engine to make unstable the combustion state of theengine.

(f3) Further, since the continuous-time system model is used as acontrolled object model, it is difficult to directly identify modelparameters of the controlled object model from experimental data of thecontrolled object. For this reason, it is necessary, more specifically,to approximately transform the continuous-time system model to adiscrete-time system model to identify the model parameters based on thediscrete-time system model. The use of such approximate transformdegrades the accuracy of identification of the model parameters.Furthermore, it is required to approximately transform the discrete-timesystem model to the continuous-time system model again, which causes anincrease in modeling errors occurring in modeling the controlled object.Consequently, to ensure a large margin of the stability of the control,it is necessary to reduce the controller gain, resulting in furtherdegraded controllability. In short, the control system proposed inPatent Literature 1 cannot ensure the robustness and theresponse-specifying characteristics peculiar to the sliding modecontrol.

To solve the above described problems in Patent Literature 1, it iscontemplated to apply the control method in Patent Literature 2 to thecontrol system proposed in Patent Literature 1. In this case, althoughthe above-described problems (f1) to (f3) in Patent Literature 1 can besolved, since the control method in Patent Literature 2 calculates thecompensation value by the onboard identifier, it is impossible to solvethe problem (f2) until the number of times of the calculation reaches apredetermined value. In short, it takes some time to compensate for andsuppress the influence of the periodic disturbance, which can degradethe stability and the accuracy of the control during the time.

SUMMARY OF THE INVENTION

It is a first object of the invention to provide a control system whichis capable of compensating for and suppressing the influence of aperiodic disturbance on a controlled object more quickly, even when thecontrolled object is subjected to the periodic disturbance the amplitudeof which periodically changes, thereby enhancing the stability and theaccuracy of control.

It is a second object of the invention to provide a control system whichis capable of compensating for and suppressing the influence of aperiodic disturbance on a moving part-driving mechanism more quickly,thereby enhancing the stability and the accuracy of control.

To attain the first object, in a first aspect of the invention, there isprovided a control system for controlling an output of a controlledobject to which is applied a periodic disturbance an amplitude of whichperiodically changes, by a control input, comprising disturbancecompensation value-storing means for storing a plurality of disturbancecompensation values for compensating for the periodic disturbance, thedisturbance compensation values having been set in advance in timeseries according to a result of prediction of a change in the amplitudeof the periodic disturbance, disturbance compensation value-selectingmeans for selecting, in timing of selection at a repetition periodcorresponding to 1/n (n is an integer not smaller than 2) of arepetition period of occurrence of the periodic disturbance, onedisturbance compensation value corresponding to the timing of selection,from the stored disturbance compensation values, and controlinput-calculating means for calculating the control input, with apredetermined control algorithm, according to the selected disturbancecompensation value.

With the configuration of this control system, a plurality ofdisturbance compensation values for compensating for a periodicdisturbance are set in advance in time series according to a result ofprediction of a change in the amplitude of the periodic disturbance, andstored in disturbance compensation value-storing means. From the storeddisturbance compensation values, in timing of selection at a repetitionperiod corresponding to 1/n of a repetition period of occurrence of theperiodic disturbance, one disturbance compensation value correspondingto the timing of selection is selected, and the control input iscalculated, with a predetermined control algorithm, according to theselected disturbance compensation value. Thus, one disturbancecompensation value is only selected in the timing of selection from thedisturbance compensation values set in advance, and the control input iscalculated according to the selected disturbance compensation value withthe predetermined control algorithm. Therefore, the output of thecontrolled object is controlled by the control input thus calculated,whereby it is possible to compensate for and suppress the influence ofthe periodic disturbance on the output of the controlled object morequickly than the prior art. This makes it possible to enhance thestability and the accuracy of control. It should be noted throughout thespecification, “to store the disturbance compensation values” includesnot only to store the disturbance compensation values in a memory or thelike but also to hold them within the control system. Further, “tocalculate” e.g. in “to calculate the control input”, and “to calculatethe disturbance estimation value” includes not only to compute by aprogram but also to generate an electric signal indicative thereof by anelectric circuit.

To attain the above object, in a second aspect of the invention, thereis provided a control system for controlling an output of a controlledobject to which is applied a periodic disturbance an amplitude of whichperiodically changes, by a control input, comprising disturbancecompensation value-storing means for storing a plurality of disturbancecompensation values for compensating for the periodic disturbance, thedisturbance compensation values having been set in advance in timeseries according to a result of prediction of a change in the amplitudeof the periodic disturbance, disturbance compensation value-selectingmeans for selecting, in timing of selection at a repetition periodcorresponding to 1/n (n is an integer not smaller than 2) of arepetition period of occurrence of the periodic disturbance, onedisturbance compensation value corresponding to the timing of selection,from the stored disturbance compensation values, disturbance estimationvalue-calculating means for calculating a disturbance estimation valuefor compensating for a disturbance and modeling errors in the controlledobject, with a predetermined estimation algorithm based on a modeldefining relationships between the disturbance estimation value, thecontrol input, and the output of the controlled object, and controlinput-calculating means for calculating the control input, with apredetermined control algorithm, according to the selected disturbancecompensation value.

With the configuration of this control system, a plurality ofdisturbance compensation values for compensating for a periodicdisturbance are set in advance in time series according to a result ofprediction of a change in the amplitude of the periodic disturbance, andstored in disturbance compensation value-storing means. From theplurality of stored disturbance compensation values, in timing ofselection at a repetition period corresponding to 1/n of a repetitionperiod of occurrence of the periodic disturbance, one disturbancecompensation value corresponding to the timing of selection is selected,and a disturbance estimation value for compensating for the disturbanceand modeling errors in the controlled object is calculated with apredetermined estimation algorithm based on a model definingrelationships between the disturbance estimation value, the controlinput, and the output of the controlled object. Further, the controlinput is calculated with a predetermined control algorithm according tothe selected disturbance compensation value and the calculateddisturbance estimation value. Thus, one disturbance compensation valueis only selected in the timing of selection from the disturbancecompensation values set in advance, and the control input is calculatedaccording to the selected disturbance compensation value. Therefore, asdescribed above, the output of the controlled object is controlled bythe control input thus calculated, whereby it is possible to compensatefor and suppress the influence of the periodic disturbance on the outputof the controlled object more quickly than the prior art. Moreover,since the control input is calculated further according to thedisturbance estimation value, it is possible to properly compensate forthe steady-state disturbance in the controlled object and the modelingerrors, thereby making it possible to control the output of thecontrolled object such that the steady-state deviation is not produced.This makes it possible to markedly enhance the stability and theaccuracy of the control.

To attain the above object, in a third aspect of the invention, there isprovided a control system for controlling an output of a controlledobject to which is applied a periodic disturbance an amplitude of whichperiodically changes, by a control input, comprising disturbancecompensation value-storing means for storing a plurality of disturbancecompensation values for compensating for the periodic disturbance, thedisturbance compensation values having been set in advance in timeseries according to a result of prediction of a change in the amplitudeof the periodic disturbance, disturbance compensation value-selectingmeans for selecting, in timing of selection at a repetition periodcorresponding to 1/n (n is an integer not smaller than 2) of arepetition period of occurrence of the periodic disturbance, onedisturbance compensation value corresponding to the timing of selection,from the stored disturbance compensation values, modelparameter-identifying means for identifying model parameters of a modeldefining relationships between the disturbance compensation value, thecontrol input, and the output of the controlled object, with apredetermined identification algorithm, and control input-calculatingmeans for calculating the control input, with a predetermined algorithmincluding a predetermined control algorithm based on the model,according to the identified model parameters and the selecteddisturbance compensation value.

With the configuration of this control system, a plurality ofdisturbance compensation values for compensating for a periodicdisturbance are set in advance in time series according to a result ofprediction of a change in the amplitude of the periodic disturbance, andstored in disturbance compensation value-storing means. From the storeddisturbance compensation values, in timing of selection at a repetitionperiod of selection, corresponding to 1/n of a repetition period ofoccurrence of the periodic disturbance, one disturbance compensationvalue corresponding to the timing of selection is selected, and modelparameters of a model defining the relationships between the selecteddisturbance compensation value, the control input, and the output of thecontrolled object are identified with a predetermined identificationalgorithm. Then, the control input is calculated with a predeterminedalgorithm including a predetermined control algorithm based on themodel, according to the identified model parameters and the selecteddisturbance compensation value. Thus, one disturbance compensation valueis only selected in the timing of selection from the disturbancecompensation values set in advance, and the control input is calculatedaccording to the selected disturbance compensation value. Therefore, asdescribed above, the output of the controlled object is controlled bythe control input thus calculated, whereby it is possible to compensatefor and suppress the influence of the periodic disturbance on the outputof the controlled object more quickly than the prior art. Moreover, thecontrol input is calculated further according to the identified valuesof model parameters of the model defining the relationships between thedisturbance compensation value, the control input, and the output of thecontrolled object, and hence the control input can be calculated usingthe model parameters identified such that they are not adverselyaffected by the periodic disturbance, whereby even when the dynamiccharacteristics of the controlled object change, it is possible tocontrol the output of the controlled object, while quickly absorbing theinfluence of the change. This makes it possible to markedly enhance thestability and the accuracy of the control.

To attain the above object, in a fourth aspect of the invention, thereis provided a control system for controlling an output of a controlledobject to which is applied a periodic disturbance an amplitude of whichperiodically changes, by a control input, comprising disturbancecompensation value-storing means for storing a plurality of disturbancecompensation values for compensating for the periodic disturbance, thedisturbance compensation values having been set in advance in timeseries according to a result of prediction of a change in the amplitudeof the periodic disturbance, disturbance compensation value-selectingmeans for selecting, in timing of selection at a repetition periodcorresponding to 1/n (n is an integer not smaller than 2) of arepetition period of occurrence of the periodic disturbance, onedisturbance compensation value corresponding to the timing of selection,from the stored disturbance compensation values, amplitude correctionvalue-calculating means for calculating an amplitude correction valuefor correcting an amplitude of the disturbance compensation value, witha predetermined algorithm based on a model defining relationshipsbetween the amplitude correction value, the disturbance compensationvalue, the control input, and the output of the controlled object, andcontrol input-calculating means for calculating the control input, witha predetermined control algorithm, according to the calculated amplitudecorrection value and the selected disturbance compensation value.

With the configuration of this control system, a plurality ofdisturbance compensation values for compensating for a periodicdisturbance are set in advance in time series according to a result ofprediction of a change in the amplitude of the periodic disturbance, andstored in disturbance compensation value-storing means. From the storeddisturbance compensation values, in the timing of selection at arepetition period corresponding to 1/n of a repetition period ofoccurrence of the periodic disturbance, one disturbance compensationvalue corresponding to the timing of selection is selected. Then, anamplitude correction value for correcting an amplitude of thedisturbance compensation value is calculated with a predeterminedalgorithm based on a model defining the relationships between theamplitude correction value, the selected disturbance compensation value,the control input, and the output of the controlled object, and thecontrol input is calculated with a predetermined control algorithmaccording to the calculated amplitude correction value and the selecteddisturbance compensation value. As described above, one disturbancecompensation value is only selected in the timing of selection from thedisturbance compensation values set in advance, and the control input iscalculated according to the selected disturbance compensation value.Therefore, by controlling the output of the controlled object by thecontrol input thus calculated, as described above, it is possible tocompensate for and suppress the influence of the periodic disturbance onthe output of the controlled object more quickly than the prior art.Moreover, the control input is calculated further according to theamplitude correction value, so that even when a difference occursbetween the amplitude of the disturbance compensation value and theamplitude of an actual periodic disturbance, such a difference can becompensated for. From the above, it is possible to enhance the stabilityand the accuracy of the control.

Preferably, the control system further comprises target value-settingmeans for setting a target value of the output of the controlled object,and the predetermined control algorithm includes a response-specifyingcontrol algorithm for causing the output of the controlled object toconverge to the target value.

With the configuration of this preferred embodiment, the control inputis calculated with the predetermined control algorithm including aresponse-specifying control algorithm for causing the output of thecontrolled object to converge to a target value, and hence even whenthere occurs a large difference between the output of the controlledobject and the target value, the output of the controlled object can becaused to converge to the target value quickly and accurately whileavoiding overshooting due to the large difference. This makes itpossible to further enhance the stability and the accuracy of thecontrol.

Preferably, the control system further comprises target value-settingmeans for setting a target value of the output of the controlled object,and the predetermined control algorithm includes a two-degree-of-freedomcontrol algorithm for causing the output of the controlled object toconverge to the target value.

With the configuration of this preferred embodiment, the control inputis calculated with the predetermined control algorithm including atwo-degree-of-freedom control algorithm for causing the output of thecontrolled object to converge to a target value, and hence even when thetarget value is largely changed, the output of the controlled object canbe caused to converge to the target value stably and accurately whileavoiding overshooting due to the change. This makes it possible tofurther enhance the stability and the accuracy of the control.

Preferably, the controlled object includes a variable cam phasemechanism for changing a cam phase, the cam phase being defined as atleast one of a phase of an intake camshaft and a phase of an exhaustcamshaft of an internal combustion engine with respect to a crankshaft,the output of the controlled object being the cam phase changed by thevariable cam phase mechanism, and the control input is inputted to thevariable cam phase mechanism.

With the configuration of this preferred embodiment, it is possible tocontrol the cam phase, while compensating for and suppressing theinfluence of the periodic disturbance on the cam phase more quickly thanthe prior art. This makes it possible to prevent the intake air amountfrom being changed due to the periodic disturbance when at least one ofeach intake valve and each exhaust valve is opened. This makes itpossible to avoid a change in torque generated by the engine to ensure astable combustion state of the engine.

Preferably, the controlled object includes a variable valve liftmechanism for changing a valve lift, the valve lift being defined as atleast one of a lift of intake valves and a lift of exhaust valves of aninternal combustion engine, and the output of the controlled objectbeing the valve lift changed by the variable valve lift mechanism, andthe control input is inputted to the variable valve lift mechanism.

Generally, when the variable valve lift mechanism is subjected to theperiodic disturbance, at least one of the lift of intake valves and thelift of exhaust valves is changed by the influence of the periodicdisturbance, to change the intake air amount when they are opened. Thiscauses a change in torque generated by the engine to make unstable thecombustion state of the engine. In view of this, with the configurationof this preferred embodiment, it is possible to control the lift of eachintake valve and/or each exhaust valve, while compensating for andsuppressing the influence of the periodic disturbance on the cam phasemore quickly than the prior art. This makes it possible to prevent theintake air amount from being changed by the periodic disturbance wheneach intake valve and/or each exhaust valve are/is opened, therebymaking it possible to avoid the change in torque generated by the engineto ensure a stable combustion state of the engine.

Preferably, the controlled object includes a variable compression ratiomechanism for changing a compression ratio of an internal combustionengine, the output of the controlled object being the compression ratiochanged by the variable compression ratio mechanism, and the controlinput is inputted to the variable compression ratio mechanism.

Generally, when the variable compression ratio mechanism is subjected tothe periodic disturbance, a compression ratio is changed due to theinfluence of the periodic disturbance, to thereby degrade compatibilitybetween the compression ratio and the ignition timing. This can causeoccurrence of knocking and degradation of combustion efficiency. In viewof this, with the configuration of this preferred embodiment, it ispossible to control the compression ratio, while compensating for andsuppressing the influence of the periodic disturbance on the cam phasemore quickly than the prior art. This makes it possible to prevent thecompression ratio from being changed by the influence of the periodicdisturbance, to thereby maintain excellent compatibility between thecompression ratio and the ignition timing. As a result, it is possibleto avoid occurrence of knocking and reduction of combustion efficiency.

To attain the second object, in a fifth aspect of the invention, thereis provided a control system for a moving part-driving mechanism whichchanges at least one of operation timing and an operation amount of amoving part of an internal combustion engine, and to which is applied aperiodic disturbance an amplitude of which periodically changes alongwith rotation of a crankshaft of the engine, comprising disturbancecompensation value-storing means for storing a plurality of disturbancecompensation values for compensating for the periodic disturbance, thedisturbance compensation values having been set in advance according toa result of prediction of a change in amplitude of the periodicdisturbance caused by the rotation of the crankshaft, disturbancecompensation value-selecting means for selecting, in timing of selectioncorresponding to each rotation of the crankshaft of the engine through apredetermined angle, a disturbance compensation value corresponding tothe timing of selection from the stored disturbance compensation values,and control input-calculating means for calculating a control input forcontrol of the moving part-driving mechanism, with a predeterminedcontrol algorithm, according to the selected disturbance compensationvalue.

With the configuration of this control system, a plurality ofdisturbance compensation values for compensating for a periodicdisturbance are set in advance according to a result of prediction of achange in amplitude of the periodic disturbance, and stored indisturbance compensation value-storing means, and from the disturbancecompensation values in the timing of selection corresponding to eachrotation of the crankshaft of the engine through a predetermined angle,a disturbance compensation value corresponding to the timing ofselection is selected, so that by properly setting the predeterminedangle, the disturbance compensation value can be selected as a valuecapable of compensating for the periodic disturbance properly andquickly. Further, it is only required to select a disturbancecompensation value, and the control input for control of the movingpart-driving mechanism is calculated with a predetermined algorithmaccording to the disturbance compensation value thus selected, and henceif the moving part-driving mechanism is controlled using the controlinput calculated as above, it is possible to compensate for and suppressthe influence of the periodic disturbance on at least one of theoperation timing and the operation amount of the moving part morequickly than the prior art. This makes it possible to enhance thestability and the accuracy of control of the moving part-drivingmechanism.

Preferably, the moving part-driving mechanism includes a variable camphase mechanism for changing a cam phase as the operation timing of themoving part, the camp phase being defined as at least one of a phase ofan intake camshaft and a phase of an exhaust camshaft of the engine withrespect to the crankshaft.

With the configuration of this preferred embodiment, the movingpart-driving mechanism includes a variable cam phase mechanism forchanging a cam phase as the operation timing of the moving part, andhence by controlling the variable cam phase mechanism using the controlinput calculated according to the disturbance compensation value, it ispossible to compensate for and suppress the influence of the periodicdisturbance on the variable cam phase mechanism more quickly than theprior art, thereby making it possible to enhance the stability and theaccuracy of the control. When the variable cam phase mechanism isapplied to a type for changing the cam phase of intake camshaft,differently from the prior art, it is possible to prevent the wholevalve open time period of each intake valve from being shortened by theinfluence of the periodic disturbance, thereby making it possible toavoid the amount of intake air from being reduced when the intake valveis opened. This makes it possible to properly ensure torque generated bythe engine to ensure a stable combustion state of the engine. Further,when the variable cam phase mechanism is applied to a type for changingthe cam phase of the exhaust camshaft, it is possible to prevent thewhole valve open time period of each exhaust valve from being shortenedby the influence of the periodic disturbance, thereby making it possibleto avoid reduction of the internal EGR amount. This makes it possible toensure a stable combustion state of the engine.

Preferably, the disturbance compensation value-selecting means selectsthe disturbance compensation value further according to a cam phaseparameter indicative of the cam phase.

Generally, when the variable cam phase mechanism is provided in theengine, when the cam phase is changed by the variable cam phasemechanism, the phase of the periodic disturbance applied to the variablecam phase mechanism is also changed. In view of this, with theconfiguration of this preferred embodiment, since the disturbancecompensation value is selected further according to a cam phaseparameter indicative of the cam phase, it is possible to select thedisturbance compensation value as a value capable of properlycompensating for a change in the cam phase of the periodic disturbance,caused by the change in the cam phase. This makes it possible to furtherenhance the stability and the accuracy of the control.

Preferably, the engine includes a variable valve lift mechanism forchanging a valve lift, the valve lift being defined as at least one of alift of intake valves and a lift of exhaust valves of the engine, andthe disturbance compensation values being set further according toresults being prediction of at least one of the change in the amplitudeand a change in a behavior of the periodic disturbance, caused by achange in the valve lift by the variable valve lift mechanism, and thedisturbance compensation value-selecting means selects the disturbancecompensation value further according to a valve lift parameterindicative of the valve lift.

Generally, when the variable valve lift mechanism is provided in theengine, when the valve lift is changed by the variable valve liftmechanism, at least one of the amplitude and the behavior of theperiodic disturbance applied to the variable cam phase mechanism is alsochanged. In view of this, with the configuration of this preferredembodiment, the disturbance compensation values are set furtheraccording to a result of prediction of at least one of a change in theamplitude and a change in the behavior of the periodic disturbance,caused by the change in the valve lift by the variable valve liftmechanism, and the disturbance compensation value is selected furtheraccording to a valve lift parameter indicative of the valve lift.Therefore, the disturbance compensation value can be selected as a valuecapable of properly compensating for at least one of the change in theamplitude and the change in the behavior of the periodic disturbance,caused by the change in the valve lift. This makes it possible tofurther enhance the stability and the accuracy of the control.

Preferably, the control input-calculating means corrects the disturbancecompensation value according to a rotational speed of the engine, andcalculates the control input according to the corrected disturbancecompensation value.

Generally, when the rotational speed of the engine is changed, thefrequency of the periodic disturbance applied to the variable cam phasemechanism is also changed. In view of this, with the configuration ofthis preferred embodiment, since the disturbance compensation value iscorrected according to the rotational speed of the engine, the change inthe frequency of the periodic disturbance, caused by the change in therotational speed of the engine, can be reflected on the correcteddisturbance compensation value. Further, since the control input iscalculated according to the disturbance compensation value thuscorrected, it is possible to control the variable cam phase mechanism,while properly compensating for the change in the frequency of theperiodic disturbance, caused by the change in the rotational speed ofthe engine.

Preferably, the control input-calculating means calculates the controlinput irrespective of the disturbance compensation value, when therotational speed of the engine is not lower than a predeterminedrotational speed.

When the disturbance compensation value is selected in the timing ofselection corresponding to each rotation of the crankshaft of the enginethrough the predetermined angle, if the rotational speed of the enginebecomes high, an interval of the timing for selecting the disturbancecompensation value, that is, a repetition period of selecting thedisturbance compensation value becomes very short. When the controlinput is calculated using the disturbance compensation value selected atsuch a short repetition period, the disturbance cannot be properlycompensated for due to low responsiveness of the variable cam phasemechanism, which can degrade controllability. In view of this, with theconfiguration of this preferred embodiment, the control input iscalculated irrespective of the disturbance compensation value when therotational speed of the engine is not lower than a predeterminedrotational speed, so that by setting the predetermined rotational speedto an appropriate speed, it is possible to control the variable camphase mechanism without degrading the controllability in a highrotational speed region.

Preferably, the control system further includes target cam phase-settingmeans for setting a target cam phase as a target of the cam phase, andthe predetermined control algorithm includes a predeterminedresponse-specifying control algorithm for causing the cam phase toconverge to the target cam phase.

With the configuration of this preferred embodiment, the control inputis calculated with the control algorithm including a response-specifyingcontrol algorithm for causing the cam phase to converge to a target camphase, and hence even when there occurs a large difference between thecam phase and the target cam phase, the cam phase can be caused toconverge to the target cam phase quickly and accurately while avoidingovershooting due to the large difference. This makes it possible tomarkedly enhance the stability and the accuracy of the control.

Preferably, the control system further includes disturbance estimationvalue-calculating means for calculating a disturbance estimation valuefor compensating for a disturbance and modeling errors in the variablecam phase mechanism, with a predetermined estimation algorithm based ona model defining relationships between the disturbance estimation value,the control input, and the cam phase, and the control input-calculatingmeans calculates the control input further according to the calculateddisturbance estimation value.

With the configuration of this preferred embodiment, a disturbanceestimation value for compensating for the disturbance and modelingerrors in the variable cam phase mechanism is calculated with apredetermined estimation algorithm based on a model defining therelationships between the disturbance estimation value, the controlinput, and the cam phase, and the control input is calculated furtheraccording to the calculated disturbance estimation value. Therefore, itis possible to properly compensate for a steady-state disturbance actingon the variable cam phase mechanism, and modeling errors in the camphase control, thereby enabling the cam phase to be controlled such thata steady-state deviation is not produced. This makes it possible tomarkedly enhance the stability and the accuracy of the control.

Preferably, the control system further includes modelparameter-identifying means for identifying model parameters of a modeldefining relationships between the disturbance compensation value, thecontrol input, and the cam phase, with a predetermined identificationalgorithm, and the control input-calculating means calculates thecontrol input with the predetermined control algorithm including apredetermined algorithm formed based on the model, according to theidentified model parameters.

With the configuration of this preferred embodiment, model parameters ofa model defining the relationships between the disturbance compensationvalue, the control input, and the cam phase are identified with apredetermined identification algorithm, and the control input iscalculated with the predetermined control algorithm including apredetermined algorithm based on the model, according to the identifiedmodel parameters. Therefore, even when the dynamic characteristics ofthe variable cam phase mechanism change, it is possible to control thevariable cam phase mechanism, while quickly absorbing the influence ofthe change in the dynamic characteristics of the variable cam phasemechanism. This makes it possible to markedly enhance the stability andthe accuracy of the control.

Preferably, the moving part-driving mechanism includes a variable valvelift mechanism for changing a valve lift as the operation amount of themoving part, the valve lift being defined as at least one of a lift ofintake valves and a lift of exhaust valves of the engine.

With the configuration of this preferred embodiment, since the movingpart-driving mechanism includes a variable valve lift mechanism forchanging a valve lift as the operation amount of the moving part, bycontrolling the variable valve lift mechanism using the control inputcalculated according to the disturbance compensation value, it ispossible to compensate for and suppress the influence of the periodicdisturbance on the variable valve lift mechanism more quickly than theprior art, thereby making it possible to enhance the stability and theaccuracy of control of the variable valve lift mechanism. This makes itpossible to prevent the lift of each intake valve and/or each exhaustvalve from being changed by the influence of the periodic disturbance,thereby making it possible to prevent the intake air amount and/or theinternal EGR amount from being changed when the valves are opened. As aresult, it is possible to properly ensure torque generated by the engineto ensure a stable combustion state of the engine.

Preferably, the disturbance compensation value-selecting means selectsthe disturbance compensation value further according to a valve liftparameter indicative of the valve lift.

Generally, when the variable valve lift mechanism is provided in theengine, when the valve lift is changed by the variable valve liftmechanism, the amplitude of the periodic disturbance applied to thevariable valve lift mechanism is also changed. In view of this, with theconfiguration of this preferred embodiment, the disturbance compensationvalue is selected further according to a valve lift parameter indicativeof the valve lift, and hence the disturbance compensation value can beselected as a value capable of properly compensating for the change inthe amplitude of the periodic disturbance, caused by the change in thevalve lift. This makes it possible to further enhance the stability andthe accuracy of the control of the variable valve lift mechanism.

Preferably, the engine includes a variable cam phase mechanism forchanging a cam phase, the cam phase being defined as at least one of aphase of an intake camshaft and a phase of an exhaust camshaft of theengine with respect to the crankshaft, and the disturbance compensationvalue-selecting means selects the disturbance compensation value furtheraccording to a cam phase parameter indicative of the cam phase.

Generally, when the variable cam phase mechanism is provided in theengine, when the cam phase is changed by the variable cam phasemechanism, the phase of the periodic disturbance applied to the variablevalve lift mechanism is also changed. In view of this, with theconfiguration of this preferred embodiment, the disturbance compensationvalue is selected further according to a cam phase parameter indicativeof the cam phase, so that the disturbance compensation value can beselected as a value capable of properly compensating for the change inthe phase of the periodic disturbance, caused by the change in the camphase. This makes it possible to further enhance the stability and theaccuracy of the control of the variable valve lift mechanism.

Preferably, the control input-calculating means corrects the disturbancecompensation value according to a rotational speed of the engine, andcalculates the control input according to the corrected disturbancecompensation value.

Generally, when the rotational speed of the engine is changed, thefrequency of the periodic disturbance applied to the variable valve liftmechanism is also changed. In view of this, with the configuration ofthis preferred embodiment, since the disturbance compensation value iscorrected according to the rotational speed of the engine, the change inthe frequency of the periodic disturbance, caused by the change in therotational speed of the engine can be reflected on the correcteddisturbance compensation value. Further, since the control input iscalculated according to the disturbance compensation value thuscorrected, it is possible to control the variable valve lift mechanism,while properly compensating for the change in the frequency of theperiodic disturbance, caused by the change in the rotational speed ofthe engine.

Preferably, the control input-calculating means calculates the controlinput irrespective of the disturbance compensation value, when therotational speed of the engine is not lower than a predeterminedrotational speed.

When the disturbance compensation value is selected in the timing ofselection corresponding to each rotation of the crankshaft of the enginethrough a predetermined angle, if the rotational speed of the enginebecomes high, the interval of the timing for selecting the disturbancecompensation value, that is, the repetition period of selecting thedisturbance compensation value becomes very short. When the controlinput is calculated using the disturbance compensation value selected atsuch a short repetition period, the disturbance cannot be properlycompensated for due to low responsiveness of the variable valve liftmechanism, which can degrade controllability of the control system. Inview of this, with the configuration of this preferred embodiment, thecontrol input is calculated irrespective of the disturbance compensationvalue, when the rotational speed of the engine is not lower than apredetermined rotational speed, and hence by setting the predeterminedrotational speed to an appropriate speed, it is possible to control thevariable valve lift mechanism without degrading the controllability in ahigh rotational speed region.

Preferably, the control system further includes target valvelift-setting means for setting a target valve lift as a target of thevalve lift, and the predetermined control algorithm includes apredetermined response-specifying control algorithm for causing thevalve lift to converge to the target valve lift.

With the configuration of this preferred embodiment, the control inputis calculated with the predetermined control algorithm including apredetermined response-specifying control algorithm for causing thevalve lift to converge to the target valve lift, and hence even whenthere occurs a large difference between the valve lift and the targetvalve lift, the valve lift can be caused to converge to the target valvelift quickly and accurately while avoiding overshooting due to the largedifference. This makes it possible to markedly enhance the stability andthe accuracy of the control.

Preferably, the control system further includes disturbance estimationvalue-calculating means for calculating a disturbance estimation valuefor compensating for a disturbance and modeling errors in the variablevalve lift mechanism, with a predetermined estimation algorithm based ona model defining relationships between the disturbance estimation value,the control input, and the valve lift, and the control input-calculatingmeans calculates the control input further according to the calculateddisturbance estimation value.

With the configuration of this preferred embodiment, a disturbanceestimation value for compensating for a disturbance and modeling errorsin the variable valve lift mechanism is calculated with a predeterminedestimation algorithm based on a model defining the relationships betweenthe disturbance estimation value, the control input, and the valve lift,and the control input is calculated further according to the calculateddisturbance estimation value. Therefore, it is possible to properlycompensate for a steady-state disturbance acting on the variable valvelift mechanism, and modeling errors in the valve lift control, therebyenabling the valve lift to be controlled such that a steady-statedeviation is not produced. This makes it possible to markedly enhancethe stability and the accuracy of the control.

Preferably, the control system further includes modelparameter-identifying means for identifying model parameters of a modeldefining relationships between the disturbance compensation value, thecontrol input, and the valve lift, with a predetermined identificationalgorithm, and the control input-calculating means calculates thecontrol input with the predetermined control algorithm including apredetermined algorithm formed based on the model, according to theidentified model parameters.

With the configuration of this preferred embodiment, model parameters ofa model defining the relationships between the disturbance compensationvalue, the control input, and the valve lift are identified with apredetermined identification algorithm, and the control input iscalculated with the predetermined control algorithm including apredetermined algorithm based on the model, according to the identifiedmodel parameters. Therefore, even when the dynamic characteristics ofthe variable valve lift mechanism change, it is possible to control thevariable valve lift mechanism, while quickly absorbing the influence ofthe change in the dynamic characteristics of the variable cam phasemechanism. This makes it possible to markedly enhance the stability andthe accuracy of the control.

Preferably, the moving part-driving mechanism includes a variablecompression ratio mechanism for changing a compression ratio of theengine by changing a stroke of pistons of the engine as the operationamount of the moving part.

Generally, in the case of a variable compression ratio mechanism, whenthe periodic disturbance is applied thereto, a compression ratio ischanged by the influence of the periodic disturbance to thereby degradecompatibility between the compression ratio and the ignition timing,which can cause occurrence of knocking and degradation of combustionefficiency. In view of this, with the configuration of this preferredembodiment, by controlling the variable compression ratio mechanismusing the control input calculated according to the disturbancecompensation value, it is possible to compensate for and suppress theinfluence of the periodic disturbance on the variable compression ratiomechanism more quickly than the prior art. Therefore, it possible toprevent the compression ratio from being changed by the influence of theperiodic disturbance, thereby making it possible to maintain excellentcompatibility between the compression ratio and the ignition timing.This makes it possible to avoid occurrence of knocking and degradationof combustion efficiency to thereby ensure a stable combustion state ofthe engine.

Preferably, the disturbance compensation value-selecting means selectsthe disturbance compensation value further according to a compressionratio parameter indicative of the compression ratio.

Generally, when the variable compression ratio mechanism is provided inthe engine, when the compression ratio is changed by the variablecompression ratio mechanism, the amplitude of the periodic disturbanceapplied to the variable compression ratio mechanism is also changed. Inview of this, with the configuration of this preferred embodiment, thedisturbance compensation value is selected further according to acompression ratio parameter indicative of the compression ratio, andhence the disturbance compensation value can be selected as a valuecapable of properly compensating for the change in the amplitude of theperiodic disturbance, caused by the change in the compression ratio.This makes it possible to further enhance the stability and the accuracyof control of the variable compression ratio mechanism.

Preferably, the control input-calculating means corrects the disturbancecompensation value according to a rotational speed of the engine, andcalculates the control input according to the corrected disturbancecompensation value.

Generally, when the rotational speed of the engine is changed, thefrequency of the periodic disturbance applied to the variablecompression ratio mechanism is also changed. In view of this, with theconfiguration of this preferred embodiment, since the disturbancecompensation value is corrected according to the rotational speed of theengine, the change in the frequency of the periodic disturbance, causedby the change in the rotational speed of the engine can be reflected onthe corrected disturbance compensation value. Further, since the controlinput is calculated according to the disturbance compensation value thuscorrected, it is possible to control the variable compression ratiomechanism, while properly compensating for the change in the frequencyof the periodic disturbance, caused by the change in the rotationalspeed of the engine.

Preferably, the control input-calculating means corrects the disturbancecompensation value according to load parameters indicative of load onthe engine, and calculates the control input according to the correcteddisturbance compensation value.

Generally, when load on the engine is changed, the amplitude of theperiodic disturbance applied to the variable compression ratio mechanismis also changed. In view of this, with the configuration of thispreferred embodiment, the disturbance compensation value is correctedaccording to a load parameter indicative of load on the engine, andhence the change in the frequency of the periodic disturbance, caused bythe change in the load of the engine can be reflected on the correcteddisturbance compensation value. Further, since the control input iscalculated according to the disturbance compensation value thuscorrected, it is possible to control the variable compression ratiomechanism while properly compensating for the change in the amplitude ofthe periodic disturbance, caused by the change in the load of theengine.

Preferably, the engine includes a variable cam phase mechanism forchanging a cam phase, the cam phase being defined as at least one of aphase of an intake camshaft and a phase of an exhaust camshaft of theengine with respect to the crankshaft, and the load parameter include acam phase parameter indicative of the cam phase.

Generally, when the variable cam phase mechanism is provided in theengine, when the cam phase is changed by the variable cam phasemechanism, the amplitude of the periodic disturbance applied to thevariable cam phase mechanism is also changed. In view of this, with theconfiguration of this preferred embodiment, since the load parameterincludes a cam phase parameter indicative of the cam phase, thedisturbance compensation value is corrected according to the cam phaseparameter, and hence the change in the amplitude of the periodicdisturbance, caused by the change in the cam phase of the engine can bereflected on the corrected disturbance compensation value. This makes itpossible to control the variable compression ratio mechanism whileproperly compensating for the change in the amplitude of the periodicdisturbance.

Preferably, the engine includes a variable valve lift mechanism forchanging a valve lift, the valve lift being defined as at least one of alift of intake valves and a lift of exhaust valves of the engine, andthe load parameter include a valve lift parameter indicative of thevalve lift.

Generally, when the variable valve lift mechanism is provided in theengine, when the valve lift is changed by the variable valve liftmechanism, the amplitude of the periodic disturbance applied to thevariable compression ratio mechanism is also changed. In view of this,with the configuration of this preferred embodiment, since the loadparameter includes a valve lift parameter indicative of the valve lift,the disturbance compensation value is corrected according to the valvelift parameter, and hence the change in the amplitude of the periodicdisturbance, caused by the change in the valve lift of the engine can bereflected on the corrected disturbance compensation value. This makes itpossible to control the variable compression ratio mechanism, whileproperly compensating for the change in the amplitude of the periodicdisturbance.

Preferably, the control input-calculating means calculates the controlinput irrespective of the disturbance compensation value, when therotational speed of the engine is not lower than a predeterminedrotational speed.

When the disturbance compensation value is selected in the timing ofselection corresponding to each rotation of the crankshaft of the enginethrough a predetermined angle, if the rotational speed of the enginebecomes high, the interval of the timing for selecting the disturbancecompensation value, that is, the repetition period of selecting thedisturbance compensation value becomes very short. When the controlinput is calculated using the disturbance compensation value selected atsuch a short repetition period, the disturbance cannot be properlycompensated for due to low responsiveness of the variable compressionratio mechanism, which can degrade controllability. In view of this,with the configuration of this preferred embodiment, the control inputis calculated irrespective of the disturbance compensation value whenthe rotational speed of the engine is not lower than a predeterminedrotational speed, and hence by setting the predetermined rotationalspeed to an appropriate speed, it is possible to control the variablecompression ratio mechanism without degrading the controllability in ahigh rotational speed region.

Preferably, the control system further includes target compressionratio-setting means for setting a target compression ratio as a targetof the compression ratio, and the predetermined control algorithmincludes a predetermined response-specifying control algorithm forcausing the compression ratio to converge to the target compressionratio.

With the configuration of this preferred embodiment, the control inputis calculated with the predetermined control algorithm including apredetermined response-specifying control algorithm for causing thecompression ratio to converge to the target compression ratio.Therefore, even when there occurs a large difference between thecompression ratio and the target compression ratio, the compressionratio can be caused to converge to the target compression ratio quicklyand accurately while avoiding overshooting due to the large difference.This makes it possible to markedly enhance the stability and theaccuracy of the control.

Preferably, the control system further includes disturbance estimationvalue-calculating means for calculating a disturbance estimation valuefor compensating for a disturbance and modeling errors in the variablecompression ratio mechanism, with a predetermined estimation algorithmbased on a model defining relationships between the disturbanceestimation value, the control input, and the compression ratio, and thecontrol input-calculating means calculates the control input furtheraccording to the calculated disturbance estimation value.

With the configuration of this preferred embodiment, a disturbanceestimation value for compensating for a disturbance and modeling errorsin the variable compression ratio mechanism is calculated with apredetermined estimation algorithm based on a model defining therelationships between the disturbance estimation value, the controlinput, and the compression ratio, and the control input is calculatedfurther according to the calculated disturbance estimation value.Therefore, it is possible to properly compensate for a steady-statedisturbance acting on the variable compression ratio mechanism, andmodeling errors in the compression ratio control, thereby enabling thecompression ratio to be controlled such that a steady-state deviation isnot produced. This makes it possible to markedly enhance the stabilityand the accuracy of the control.

Preferably, the control system further includes modelparameter-identifying means for identifying model parameters of a modeldefining relationships between the disturbance compensation value, thecontrol input, and the compression ratio, with a predeterminedidentification algorithm, and the control input-calculating meanscalculates the control input with the predetermined control algorithmincluding the predetermined algorithm based on the model, according tothe identified model parameters.

With the configuration of this preferred embodiment, model parameters ofa model defining the relationships between the disturbance compensationvalue, the control input, and the compression ratio are identified witha predetermined identification algorithm, and the control input iscalculated with the predetermined control algorithm including thepredetermined algorithm formed based on the model, according to theidentified model parameters. Accordingly, even when the dynamiccharacteristics of the variable compression ratio mechanism change, itis possible to control the variable compression ratio mechanism, whilequickly absorbing the influence of the change in the dynamiccharacteristics of the variable compression ratio mechanism. This makesit possible to markedly enhance the stability and the accuracy of thecontrol.

The above and other objects, features, and advantages of the presentinvention will become more apparent from the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically showing the arrangement of an internalcombustion engine to which is applied a control system according to afirst embodiment of the present invention;

FIG. 2 is a block diagram schematically showing the arrangement of thecontrol system;

FIG. 3 is a cross-sectional view schematically showing the arrangementof a variable intake valve-actuating mechanism and an exhaustvalve-actuating mechanism of the engine;

FIG. 4 is a cross-sectional view schematically showing the arrangementof a variable valve lift mechanism of the variable intakevalve-actuating mechanism;

FIG. 5A is a diagram showing a lift actuator in a state in which a shortarm thereof is in a maximum lift position;

FIG. 5B is a diagram showing the lift actuator in a state in which theshort arm thereof is in a minimum lift position;

FIG. 6A is a diagram showing an intake valve placed in an open statewhen a lower link of the variable valve lift mechanism is in a maximumlift position;

FIG. 6B is a diagram showing the intake valve placed in an open statewhen the lower link of the variable valve lift mechanism is in a minimumlift position;

FIG. 7 is a diagram showing a valve lift curve (solid line) which thevalve lift of the intake valve assumes when the lower link of thevariable valve lift mechanism is in the maximum lift position, and avalve lift curve (two-dot chain line) which the valve lift of the intakevalve assumes when the lower link of the variable valve lift mechanismis in the minimum lift position;

FIG. 8 is a diagram schematically showing the arrangement of a variablecam phase mechanism;

FIG. 9 is a diagram showing a valve lift curve (solid line) which thevalve lift of the intake valve assumes when a cam phase is set to a mostretarded value by the variable cam phase mechanism, and a valve liftcurve (two-dot chain line) which the valve lift of the intake valveassumes when the cam phase is set to a most advanced value by thevariable cam phase mechanism;

FIG. 10A is a diagram schematically showing the whole arrangement of avariable compression ratio mechanism in a state where a compressionratio is set to a low compression ratio;

FIG. 10B is a diagram schematically showing the arrangement of a controlshaft and a compression ratio actuator and their vicinity of thevariable compression ratio mechanism in a state where the compressionratio is set to a high compression ratio;

FIG. 11 is a block diagram schematically showing the arrangement of acam phase controller;

FIGS. 12A and 12B are diagrams useful in explaining a periodicdisturbance, in which

FIG. 12A is a diagram useful in explaining operation of an intake camactuating the intake valve in the valve-opening direction, and

FIG. 12B is a diagram useful in explaining operation of the intake camactuating the intake valve in the valve-closing direction;

FIG. 13 is a timing diagram showing the influence of the periodicdisturbance on cam phase control;

FIG. 14 is a diagram showing valve lift curves which the valve lift ofthe intake valve assumes when the valve lift is high, which is useful incomparing a case where a variable cam phase mechanism is provided and acase where the variable cam phase mechanism is not provided;

FIG. 15 is a diagram showing valve lift curves which the valve lift ofthe intake valve assumes when the valve lift is low, which is useful incomparing the case where the variable cam phase mechanism is providedand the case where the variable cam phase mechanism is not provided;

FIG. 16 is a diagram showing an example of a map value of a disturbancecompensation value map for use in cam phase control for one cylinder,the map value set for a maximum value of the valve lift;

FIG. 17 is a diagram showing an example of a map value of thedisturbance compensation value map for use in the cam phase control forthe one cylinder, the map value set for a minimum value of the valvelift;

FIG. 18 is a diagram showing an example of a map value of thedisturbance compensation value map for use in the cam phase control,which is calculated by a compensation element of the control systemaccording to a first embodiment in association with the maximum value ofthe valve lift:

FIG. 19 is a diagram showing an example of a map value of thedisturbance compensation value map for use in the cam phase control,which is calculated by the compensation element of the control systemaccording to the first embodiment in association with the minimum valueof the valve lift:

FIG. 20 is a diagram showing a control algorithm for atwo-degree-of-freedom sliding mode controller, and a model used forderiving the control algorithm;

FIG. 21 is a diagram showing an arithmetic expression for an additionelement, and a control algorithm for a DSM controller;

FIG. 22 s a block diagram schematically showing the configuration of avalve lift controller;

FIG. 23 is a diagram showing an example of a map value of a disturbancecompensation value map for use in valve lift control, the map value setfor a maximum value of a target valve lift;

FIG. 24 is a diagram showing an example of a map value of thedisturbance compensation value map for use in the valve lift control,the map value set for a minimum value of the target valve lift;

FIG. 25 is a block diagram schematically showing the configuration of acompression ratio controller;

FIG. 26 is a diagram showing an example of a disturbance compensationvalue map for use in retrieving a map value of a disturbancecompensation value for use in compression ratio control;

FIG. 27 is a flowchart showing a process for calculation of disturbancecompensation values for use in the cam phase control, the valve liftcontrol, and the compression ratio control;

FIG. 28 is a diagram showing an example of a table used for calculationof a correction coefficient for the cam phase control;

FIG. 29 is a diagram showing an example of a table used for calculationof a correction coefficient for the valve lift control;

FIG. 30 is a diagram showing an example of a table used for calculationof a first correction coefficient for the compression ratio control;

FIG. 31 is a diagram showing an example of a table used for calculationof a second correction coefficient for the compression ratio control;

FIG. 32 is a flowchart showing a process for calculation of a cam phasecontrol input, a lift control input, and a compression ratio input;

FIG. 33 is a diagram showing an example of a map used for calculation ofa target cam phase;

FIG. 34 is a diagram showing an example of a map used for calculation ofa target valve lift;

FIG. 35 is a diagram showing an example of a map used for calculation ofa target compression ratio;

FIG. 36 is a diagram showing an example of a result of a simulation ofthe cam phase control with respect to one cylinder by the control systemaccording to the first embodiment;

FIG. 37 is a diagram showing a variation of the disturbance compensationvalue map for use in calculation of a map value of a disturbancecompensation value for the cam phase control;

FIG. 38 is a block diagram schematically showing the configuration of acam phase controller of a control system according to a secondembodiment of the invention;

FIG. 39 is a block diagram schematically showing the configuration of avalve lift controller of the control system according to the secondembodiment;

FIG. 40 is a block diagram schematically showing the configuration of acompression ratio controller of the control system according to thesecond embodiment;

FIG. 41 is a diagram showing an algorithm for calculation of adisturbance estimation value by an adaptive disturbance observer of thecam phase controller of the control system according to the secondembodiment, and a model used for deriving the algorithm;

FIG. 42 is a diagram showing a control algorithm for atwo-degree-of-freedom sliding mode controller of the cam phasecontroller of the control system according to the second embodiment;

FIG. 43 is a diagram showing a control algorithm for a DSM controller ofthe cam phase controller of the control system according to the secondembodiment;

FIG. 44 is a block diagram schematically showing the configuration of acam phase controller of a control system according to a third embodimentof the present invention;

FIG. 45 is a block diagram schematically showing the configuration of avalve lift controller of the control system according to the thirdembodiment;

FIG. 46 is a block diagram schematically showing the configuration of acompression ratio controller of the control system according to thethird embodiment;

FIG. 47 is a diagram showing an identification algorithm for a partialparameter identifier of the cam phase controller of the control systemaccording to the third embodiment, and a model used for deriving theidentification algorithm;

FIG. 48 is a diagram showing a control algorithm for atwo-degree-of-freedom sliding mode controller of the cam phasecontroller of the control system according to the third embodiment; and

FIG. 49 is a diagram showing a control algorithm for a DSM controller ofthe cam phase controller of the control system according to the thirdembodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereafter, a control system according to a first embodiment of thepresent invention will be described with reference to drawings. Thecontrol system 1 includes an ECU 2, as shown in FIG. 2. As describedhereinafter, the ECU 2 carries out control processes, such as valve liftcontrol, cam phase control, and compression ratio control, depending onoperating conditions of an internal combustion engine (hereinaftersimply referred to as “the engine”) 3.

Referring to FIGS. 1 and 3, the engine 3 is an in-line four-cylindergasoline engine having four pairs of cylinders 3 a and pistons 3 b (onlyone pair of which is shown), and installed on a vehicle, not shown. Theengine 3 includes an intake valve 4 and an exhaust valve 7 provided foreach cylinder 3 a, for opening and closing an intake port and an exhaustport thereof, respectively, an intake camshaft 5 and intake cams 6 thatactuate the intake valves 4, a variable intake valve-actuating mechanism40 that actuates the intake valves 4 to open and close the same, anexhaust camshaft 8 and exhaust cams 9 that actuate the exhaust valves 7,an exhaust valve-actuating mechanism 30 that actuates the exhaust valves7 to open and close the same, and a variable compression ratio mechanism80 and so forth.

The intake valve 4 has a stem 4 a thereof slidably fitted in a guide 4b. The guide 4 b is rigidly fixed to a cylinder head 3 c. Further, asshown in FIG. 4, the intake valve 4 includes upper and lower springsheets 4 c and 4 d, and a valve spring 4 e disposed therebetween, and isurged by the valve spring 4 e in the valve-closing direction.

Further, the intake camshaft 5 and the exhaust camshaft 8 are rotatablymounted through the cylinder head 3 c via holders, not shown. The intakecamshaft 5 has an intake sprocket (not shown) coaxially and rotatablyfitted on one end thereof. The intake sprocket is connected to acrankshaft 3 d via a timing belt, not shown, and connected to the intakecamshaft 5 via a variable cam phase mechanism 70, described hereinafter.With the above configuration, the intake camshaft 5 performs onerotation per two rotations of the crankshaft 3 d. Further, the intakecam 6 is provided on the intake camshaft 5 on each cylinder 3 a suchthat the intake cam 6 rotates in unison with the intake camshaft 5.

Furthermore, the variable intake valve-actuating mechanism 40 isprovided for actuating the intake valve 4 of each cylinder 3 a so as toopen and close the same, in accordance with rotation of the intakecamshaft 5, and continuously changing the lift and the valve timing ofthe intake valve 4, which will be described in detail hereinafter. Itshould be noted that in the present embodiment, “the lift of the intakevalve 4” (hereinafter referred to as “the valve lift”) represents themaximum lift of the intake valve 4.

On the other hand, the exhaust valve 7 has a stem 7 a thereof slidablyfitted in a guide 7 b. The guide 7 b is rigidly fixed to the cylinderhead 3 c. Further, the exhaust valve 7 includes upper and lower springsheets 7 c and 7 d, and a valve spring 7 e disposed therebetween, and isurged by the valve spring 7 e in the valve-closing direction.

Further, the exhaust camshaft 8 has an exhaust sprocket (not shown)integrally formed therewith, and is connected to the crankshaft 3 d bythe exhaust sprocket and a timing belt, not shown, whereby the exhaustcamshaft 8 performs one rotation per two rotations of the crankshaft 3d. Further, the exhaust cam 9 is disposed on the exhaust camshaft 8 foreach cylinder 3 a such that the exhaust cam 9 rotates in unison with theexhaust camshaft 8.

Further, the exhaust valve-actuating mechanism 30 includes rocker arms31. Each rocker arm 31 is pivotally moved in accordance with rotation ofthe associated exhaust cam 9 to thereby actuate the exhaust valve 7 foropening and closing the same against the urging force of the valvespring 7 e.

The engine 3 is also provided with a crank angle position sensor 20. Thecrank angle position sensor 20 is comprised of a magnet rotor and an MRE(magnetic resistance element) pickup, and delivers a CRK signal and aTDC signal, which are both pulse signals, to the ECU 2 in accordancewith rotation of the crankshaft 3d. Each pulse of the CRK signal isgenerated whenever the crankshaft 3 d rotates through 10 degrees. TheECU 2 determines the rotational speed NE of the engine 3 (hereinafterreferred to as “the engine speed NE”) based on the CRK signal. Further,the TDC signal indicates that each piston 3 b in the associated cylinder3 a is in a predetermined crank angle position slightly before the TDCposition at the start of the intake stroke, and each pulse of the TDCsignal is generated whenever the crankshaft 3 d rotates through apredetermined crank angle.

Further, in an intake pipe 10 of the engine 3, there are arranged an airflow sensor 21, a throttle valve mechanism 11, an intake pipe absolutepressure sensor 22, a fuel injection valve 12, and so forth, fromupstream to downstream in the mentioned order at respective locations ofthe intake pipe 10.

The air flow sensor 21 is formed by a hot-wire air flow meter, fordetecting an amount GTH of intake air (hereinafter referred to as “theTH passing intake air amount GTH”) flowing through the throttle valve11, and delivers a signal indicative of the sensed TH passing intake airamount GTH to the ECU 2. Further, the throttle valve 11 is pivotallydisposed across an intermediate portion of the intake pipe 10 such thatthe degree of opening thereof is changed by the pivotal motion thereofto thereby change the TH passing intake air amount GTH. Furthermore, thethrottle valve 11 is held in a fully-open state during normal operationof the engine 3 by the ECU 2 via an actuator, not shown, and has thedegree of opening thereof controlled by the ECU 2 via the actuator whenthe variable intake valve-actuating mechanism 40 is faulty, or whennegative pressure is supplied to a master back (not shown).

A portion of the intake pipe 10 downstream of the throttle valve 11forms a surge tank 10 a into which is inserted an intake pipe absolutepressure sensor 22. The intake pipe absolute pressure sensor 22 isimplemented e.g. by a semiconductor pressure sensor, and detects anabsolute pressure PBA in the intake pipe 10 (hereinafter referred to as“the intake pipe absolute pressure PBA”), to deliver a signal indicativeof the sensed intake pipe absolute pressure PBA to the ECU 2.

The fuel injection valve 12 is driven by a drive signal supplied fromthe ECU 2, and injects fuel into the intake pipe 10. Spark plugs 13 (seeFIG. 2) are mounted through the cylinder head 3 c of the engine 3. Whena drive signal indicative of ignition timing is applied from the ECU 2,the spark plug 13 causes a spark discharge, thereby burning a mixture ina combustion chamber.

Next, a description will be given of the aforementioned variable intakevalve-actuating mechanism 40. As shown in FIG. 4, the variable intakevalve-actuating mechanism 40 is comprised of the intake camshaft 5, theintake cams 6, a variable valve lift mechanism 50, and the variable camphase mechanism 70.

The variable valve lift mechanism 50 (moving part-driving mechanism) isprovided for actuating the intake valves 4 (moving part) to open andclose the same, in accordance with rotation of the intake camshaft 5,and continuously changing the valve lift Liftin between a predeterminedmaximum value Liftinmax and a predetermined minimum value Liftinmin. Thevariable valve lift mechanism 50 is comprised of rocker arm mechanisms51 of a four joint link type, provided for the respective cylinders 3 a,and a lift actuator 60 (see FIGS. 5A and 5B) simultaneously actuatingthese rocker arm mechanisms 51.

Each rocker arm mechanism 51 is comprised of a rocker arm 52, and upperand lower links 53 and 54. The upper link 53 has one end pivotallymounted to an upper end of the rocker arm 52 by an upper pin 55, and theother end pivotally mounted to a rocker arm shaft 56. The rocker armshaft 56 is mounted through the cylinder head 3 c via holders, notshown.

Further, a roller 57 is pivotally disposed on the upper pin 55 of therocker arm 52. The roller 57 is in contact with a cam surface of theintake cam 6. As the intake cam 6 rotates, the roller 57 rolls on theintake cam 6 while being guided by the cam surface of the intake cam 6.As a result, the rocker arm 52 is vertically driven, and the upper link53 is pivotally moved about the rocker arm shaft 56.

Furthermore, an adjusting bolt 52 a is mounted to an end of the rockerarm 52 toward the intake valve 4. When the rocker arm 52 is verticallymoved in accordance with rotation of the intake cam 6, the adjustingbolt 52 a vertically drives the stem 4 a to open and close the intakevalve 4, against the urging force of the valve spring 4 e.

Further, the lower link 54 has one end pivotally mounted to a lower endof the rocker arm 52 by a lower pin 58, and the other end of the lowerlink 54 has a connection pin 59 pivotally mounted thereto. The lowerlink 54 is connected to a short arm 65, described hereinafter, of thelift actuator 60 by the connection pin 59.

On the other hand, as shown in FIGS. 5A and 5B, the lift actuator 60 iscomprised of a motor 61, a nut 62, a link 63, a long arm 64, and theshort arm 65. The motor 61 is connected to the ECU 2, and disposedoutside a head cover 3 g of the engine 3. The rotational shaft of themotor 61 is a screw shaft 61a formed with a male screw and the nut 62 isscrewed onto the screw shaft 61 a. The nut 62 is connected to the longarm 64 by the link 63. The link 63 has one end pivotally mounted to thenut 62 by a pin 63 a, and the other end pivotally mounted to one end ofthe long arm 64 by a pin 63 b.

Further, the other end of the long arm 64 is attached to one end of theshort arm 65 by a pivot shaft 66. The pivot shaft 66 is circular incross section, and extends through the head cover 3 g of the engine 3such that it is pivotally supported by the head cover 3 g. The long arm64 and the short arm 65 are pivotally moved in unison with the pivotshaft 66 in accordance with pivotal motion of the pivot shaft 66.

Furthermore, the aforementioned connection pin 59 pivotally extendsthrough the other end of the short arm 65, whereby the short arm 65 isconnected to the lower link 54 by the connection pin 59.

Next, a description will be given of operation of the variable valvelift mechanism 50 configured as above. In the variable valve liftmechanism 50, when a lift control input Uliftin, described hereinafter,is inputted from the ECU 2 to the lift actuator 60, the screw shaft 61 arotates, and the nut 62 is moved in accordance with the rotation of thescrew shaft 61 a, whereby the long arm 64 and the short arm 65 arepivotally moved about the pivot shaft 66, and in accordance with thepivotal motion of the short arm 65, the lower link 54 of the rocker armmechanism 51 is pivotally moved about the lower pin 58. That is, thelower link 54 is driven by the lift actuator 60.

In the process, under the control of the ECU 2, the range of pivotalmotion of the short arm 65 is restricted between a maximum lift positionshown in FIG. 5A and a minimum lift position shown in FIG. 5B, wherebythe range of pivotal motion of the lower link 54 is also restrictedbetween a maximum lift position indicated by a solid line in FIG. 4 anda minimum lift position indicated by a two-dot chain line in FIG. 4.

The four joint link formed by the rocker arm shaft 56, the upper andlower pins 55 and 58, and the connection pin 59 is configured such thatwhen the lower link 54 is in the maximum lift position, the distancebetween the center of the upper pin 55 and the center of the lower pin58 becomes longer than the distance between the center of the rocker armshaft 56 and the center of the connection pin 59, whereby as shown inFIG. 6A, when the intake cam 6 rotates, the amount of movement of theadjusting bolt 52 a becomes larger than the amount of movement of acontact point where the intake cam 6 and the roller 57 are in contactwith each other.

On the other hand, the four joint link is configured such that when thelower link 54 is in the minimum lift position, the distance between thecenter of the upper pin 55 and the center of the lower pin 58 becomesshorter than the distance between the center of the rocker arm shaft 56and the center of the connection pin 59, whereby as shown in FIG. 6B,when the intake cam 6 rotates, the amount of movement of the adjustingbolt 52 a becomes smaller than the amount of movement of the contactpoint where the intake cam 6 and the roller 57 are in contact with eachother.

For the above reason, when the lower link 54 is in the maximum liftposition, the intake valve 4 is opened with a larger valve lift Liftinthan when the lower link 54 is in the minimum lift position. Morespecifically, during rotation of the intake cam 6, when the lower link54 is in the maximum lift position, the intake valve 4 is openedaccording to a valve lift curve indicated by a solid line in FIG. 7, andthe valve lift Liftin assumes its maximum value Liftinmax. On the otherhand, when the lower link 54 is in the minimum lift position, the intakevalve 4 is opened according to a valve lift curve indicated by a two-dotchain line in FIG. 7, and the valve lift Liftin assumes its minimumvalue Liftinmin.

Therefore, in the variable valve lift mechanism 50, the lower link 54 ispivotally moved by the lift actuator 60 between the maximum liftposition and the minimum lift position, whereby it is possible tocontinuously change the valve lift Liftin between the maximum valueLiftinmax and the minimum value Liftinmin.

The engine 3 is provided with a pivot angle sensor 23 (see FIG. 2). Thepivot angle sensor 23 detects a pivot angle of the pivot shaft 66, i.e.the short arm 65, and delivers a signal indicative of the sensed pivotangle to the ECU 2. The ECU 2 calculates the valve lift Liftin based onthe signal output from pivot angle sensor 23.

Next, a description will be given of the aforementioned variable camphase mechanism 70 (moving part-driving mechanism). The variable camphase mechanism 70 is provided for continuously advancing or retardingthe relative phase Cain of the intake camshaft 5 as a moving part withrespect to the crankshaft 3 d (hereinafter referred to as “the cam phaseCain”), and mounted on an intake sprocket-side end of the intakecamshaft 5. As shown in FIG. 8, the variable cam phase mechanism 70includes a housing 71, a three-bladed vane 72, an oil pressure pump 73,and a solenoid valve mechanism 74.

The housing 71 is integrally formed with the intake sprocket on theintake camshaft 5 d, and divided by three partition walls 71 a formed atequal intervals. The vane 72 is coaxially mounted on the intakesprocket-side end of the intake camshaft 5, such that the vane 72radially extends outward from the intake camshaft 5, and rotatablyhoused in the housing 71. Further, the housing 71 has three advancechambers 75 and three retard chambers 76 each formed between one of thepartition walls 71 a and one of the three blades of the vane 72.

The oil pressure pump 73 is a mechanical one connected to the crankshaft3 d. As the crankshaft 3 d rotates, the oil pressure pump 73 drawslubricating oil stored in an oil pan 3 e of the engine 3 via a lowerpart of an oil passage 77 c, for pressurization, and supplies thepressurized oil to the solenoid valve mechanism 74 via the remainingpart of the oil passage 77 c.

The solenoid valve mechanism 74 is formed by combining a spool valvemechanism 74 a and a solenoid 74 b, and connected to the advancechambers 75 and the retard chambers 76 via an advance oil passage 77 aand a retard oil passage 77 b such that oil pressure supplied from theoil pressure pump 73 is outputted to the advance chambers 75 and theretard chambers 76 as advance oil pressure Pad and retard oil pressurePrt. The solenoid 74 b of the solenoid valve mechanism 74 iselectrically connected to the ECU 2. When a phase control input Ucain,referred to hereinafter, is inputted from the ECU 2, the solenoid 74 bmoves a spool valve element of the spool valve mechanism 74 a within apredetermined range of motion according to the phase control input Ucainto thereby change both the advance oil pressure Pad and the retard oilpressure Prt.

In the variable cam phase mechanism 70 constructed as above, duringoperation of the oil pressure pump 73, the solenoid valve mechanism 74is operated according to the phase control input Ucain, to supply theadvance oil pressure Pad to the advance chambers 75 and the retard oilpressure Prt to the retard chambers 76, whereby the relative phasebetween the vane 72 and the housing 71 is changed toward an advancedside or a retarded side. As a result, the cam phase Cain described aboveis continuously changed between a most retarded value Cainrt (e.g. avalue corresponding to a cam angle of 0 degrees) and a most advancedvalue Cainad (e.g. a value corresponding to a cam angle of 55 degrees),whereby valve timing of the intake valve 4 is continuously changedbetween a most retarded timing indicated by a solid line in FIG. 9 and amost advanced timing indicated by a two-dot chain line in FIG. 9.

It should be noted that the variable cam phase mechanism 70 includes alock mechanism, not shown, which locks operation of the variable camphase mechanism 70 when oil pressure supplied from the oil pressure pump73 is low. More specifically, the variable cam phase mechanism 70 isinhibited from changing the cam phase Cain, whereby the cam phase Cainis locked to a value suitable for idling or starting of the engine 3.

As described above, in the variable intake valve-actuating mechanism 40according to the present embodiment, the valve lift Liftin iscontinuously changed by the variable valve lift mechanism 50, and thecam phase Cain, i.e. the valve timing of the intahe valve 4 iscontinuously changed between the most retarded timing and the mostadvanced timing. Further, as described hereinafter, the valve liftLiftin and the cam phase Cain are controlled by the ECU 2 via thevariable valve lift mechanism 50 and the variable cam phase mechanism70, respectively.

On the other hand, a cam angle sensor 24 (see FIG. 2) is disposed at anend of the intake camshaft 5 opposite from the variable cam phasemechanism 70. The cam angle sensor 24 is implemented e.g. by a magnetrotor and an MRE pickup, for delivering a CAM signal, which is a pulsesignal, to the ECU 2 along with rotation of the intake camshaft 5. Eachpulse of the CAM signal is generated whenever the intake camshaft 5rotates through a predetermined cam angle (e.g. one degree). The ECU 2calculates the cam phase Cain based on the CAM signal and the CRK signaldescribed above.

Next the aforementioned variable compression ratio mechanism 80 (movingpart-driving mechanism) will be described with reference to FIGS. 10Aand 10B. The variable compression ratio mechanism 80 is provided forchanging a top dead center position of each piston 3 b as a moving part,that is, the stroke of the piston 3 b, to thereby continuously change acompression ratio Cr between a predetermined maximum value Crmax and apredetermined minimum value Crmin, and comprised of a composite linkmechanism 81 connected between the piston 3 b and the crankshaft 3 d, acontrol shaft 85 for controlling the motion of the composite linkmechanism 81, a compression ratio actuator 87 for driving the controlshaft 85, and so forth.

The composite link mechanism 81 is implemented by an upper link 82, alower link 83, and a control link 84. The upper link 82 corresponds to aso-called connecting rod, and has an upper end thereof pivotallyconnected to the piston 3 b via a piston pin 3 f, and a lower endthereof pivotally connected to an end of the lower link 83 via a pin 83a.

The lower link 83 has a triangular shape. Two ends of the lower link 83except for the end connected to the upper link 82 are pivotallyconnected to the crankshaft 3 d via a crank pin 83 b, and to an end ofthe control link 84 via a control pin 83 c, respectively. With the aboveconfiguration, reciprocating motion of the piston 3 b is transmitted tothe crankshaft 3 d via the composite link mechanism 81 such that it isconverted into rotating motion of the crankshaft 3 d.

Further, the control shaft 85 extends in the direction of depth(direction perpendicular to the sheet), as viewed in FIGS. 10A and 10B,similarly to the crankshaft 3 d, and includes a pivot shaft part 85 apivotally supported by a cylinder block, an eccentric shaft part 85 bintegrally formed with the pivot shaft part 85 a, and arm 86. A lowerend of the control link 84 is pivotally connected to the eccentric shaftpart 85 b. Further, a distal end of the arm 86 is formed as a fork part86 a to which is pivotally connected an end of a drive shaft 87 b of thecompression ratio actuator 87.

The compression ratio actuator 87 is formed by combining a motor and areduction mechanism (neither of which is shown), and includes a casing87 a for containing the motor and the reduction mechanism, and a driveshaft 87 b movable into and out of the casing 87 a. In the compressionratio actuator 87, when the motor is driven for normal or reverserotation by a compression ratio control input Ucr, referred tohereinafter, from the ECU 2, the drive shaft 87 b is moved between a lowcompression ratio position (position shown in FIG. 10A) where the driveshaft 87 b is most protruded from the casing 87 a, and a highcompression ratio position (position shown in FIG. 10B) where the driveshaft 87 b is most retracted toward the casing 87 a.

With the above configuration, in the variable compression ratiomechanism 80, when the drive shaft 87 b of the compression ratioactuator 87 is moved from the low compression ratio position to the highcompression ratio position, the control shaft 85 is driven via the arm86 such that it is pivotally moved counterclockwise as viewed in FIG.10A about the pivot shaft part 85 a, and the eccentric shaft part 85 bis moved downward along with the pivotal motion of the control shaft 85.As the whole control link 84 is pressed downward by the downwardmovement of the eccentric shaft part 85 b, the lower link 83 ispivotally moved clockwise as viewed in FIG. 10A about the crank pin 83b, while the upper link 82 is pivotally moved counterclockwise as viewedin FIG. 10A about the piston pin 3 f. As a result, the shape formed bythe piston pin 3 f, the upper pin 83 a, and the crank pin 83 b are madecloser to the shape of a straight line than when they are located at thelow compression ratio position, whereby the straight-line distancebetween the piston 3 f and the crank pin 83 b, obtained when the piston3 b has reached the top dead center position is increased (which meansthat the stroke of the piston 3 b is increased), to decrease the volumeof the combustion chamber, whereby the compression ratio Cr isincreased.

On the other hand, inversely to the above, when the drive shaft 87 b ofthe compression ratio actuator 87 is moved from the high compressionratio position to the low compression ratio position, the pivot shaftpart 85 a is pivotally moved clockwise as viewed in FIG. 10A, and theeccentric shaft part 85 b is moved upward along with the pivotal motionof the pivot shaft part 85 a, whereby the whole control link 84 ispushed upward. Thus, quite inversely to the above operations, the lowerlink 83 is pivotally moved counterclockwise, whereas the upper link 82is pivotally moved clockwise, as viewed in FIG. 10A. As a result, thestraight-line distance between the piston 3 f and the crank pin 83 b,obtained when the piston 3 b has reached the top dead center position isdecreased (which means that the stroke of the piston 3 b is shortened),to increase the volume of the combustion chamber, whereby thecompression ratio Cr is reduced. As described above, in the variablecompression ratio mechanism 80, by changing the pivot angle of thecontrol shaft 85, the compression ratio Cr is changed between thepredetermined maximum value Crmax and the predetermined minimum valueCrmin.

Further, the engine is provided with a control angle sensor 25 in thevicinity of the control shaft 85 (see FIG. 2). The control angle sensor25 detects a pivot angle of the control shaft 85, and delivers a signalindicative of the sensed control angle to the ECU 2. The ECU 2calculates the compression ratio Cr based on the signal output from thecontrol angle sensor 25.

Furthermore, as shown in FIG. 2, connected to the ECU 2 are anaccelerator pedal opening sensor 26, and an ignition switch (hereinafterreferred to as “the IG·SW”) 27. The accelerator pedal opening sensor 26detects a stepped-on amount AP of an accelerator pedal, not shown, ofthe vehicle (hereinafter referred to as “the accelerator pedal openingAP”) and delivers a signal indicative of the sensed accelerator pedalopening AP to the ECU 2. Further, the IG·SW 27 is turned on or off byoperation of an ignition key, not shown, and delivers a signalindicative of the ON/OFF state thereof to the ECU 2.

The ECU 2 is implemented by a microcomputer including a CPU 2 a, a RAM 2b, a ROM 2 c (disturbance compensation value-storing means), and an I/Ointerface, not shown. The ECU 2 determines operating conditions of theengine 3, based on the detection signals delivered from theabove-mentioned sensors 20 to 26, the ON/OFF signal from the IG SW 27,and the like, and executes control processes. More specifically, as willbe described in detail hereinafter, the ECU 2 controls the cam phaseCain and the valve lift Liftin via the variable cam phase mechanism 70and the variable valve lift mechanism 50, respectively, and controls thecompression ratio Cr via the variable compression ratio mechanism 80.Further, the ECU 2 controls the ignition timing of the spark plug 13according to the operating conditions of the engine 3.

It should be noted that in the present embodiment, the ECU 2 implementsdisturbance estimation value-calculating means, modelparameter-identifying means, amplitude correction value-calculatingmeans, target value-setting means, disturbance compensationvalue-storing means, disturbance compensation value-selecting means,control input-calculating means, target cam phase-setting means, targetvalve lift-setting means, and target compression ratio-setting means.Further, in the present embodiment, the cam phase Cain corresponds tooperation timing of the moving part, a cam phase parameter, and a loadparameter, and the valve lift Liftin corresponds to the amount ofoperation of the moving part, and a valve lift parameter, and a loadparameter.

Next, a description will be given of the control system 1 according tothe present embodiment. The control system 1 includes a cam phasecontroller 100 (see FIG. 11), a valve lift controller 110 (see FIG. 22),and a compression ratio controller 120 (see FIG. 25), all of which areimplemented by the ECU 2. First, a description will be given of the camphase controller 100. Referring to FIG. 11, the cam phase controller 100is comprised of a target cam phase-calculating section 101, acompensation element 102, a two-degree-of-freedom sliding modecontroller 103 (hereinafter referred to as “the two-degree-of-freedomSLD controller 103”), an addition element 104, and a DSM controller 105.

In the cam phase controller 100, as described hereinafter, the phasecontrol input Ucain is calculated, and is inputted to the variable camphase mechanism 70, whereby the cam phase Cain is controlled to a targetcam phase Cain_cmd.

First, the target cam phase-calculating section 101 (targetvalue-setting means, target cam phase-setting means) calculates thetarget cam phase Cain_cmd (target value, cam phase parameter) bysearching a map (see FIG. 33), described hereinafter, according to theengine speed NE and the accelerator pedal opening AP.

Further, the compensation element 102 (disturbance compensationvalue-storing means, disturbance compensation value-selecting means)calculates, as described hereinafter, a disturbance compensation valueRcyc_cin for the cam phase control based on the target cam phaseCain_cmd calculated by the target cam phase-calculating section 101, andother parameters.

Further, the two-degree-of-freedom SLD controller 103 (controlinput-calculating means) calculates an SLD control input Rsld for thecam phase control with a control algorithm, referred to hereinafter,according to the target cam phase Cain_cmd and the cam phase Cain.

On the other hand, the addition element 104 (control input-calculatingmeans) calculates a reference input Rsld_f (control input) for the camphase control as the sum of the disturbance compensation value Rcyc_cinfor the cam phase control, calculated by the compensation element 102,and the SLD control input Rsld for the cam phase control, calculated bythe two-degree-of-freedom SLD controller 103. Further, the DSMcontroller 105 (control input-calculating means) calculates the phasecontrol input Ucain with a control algorithm, referred to hereinafter,according to the reference input Rsld_f for the cam phase control.

Next, a description will be given of the compensation element 102. Aswill be described in detail hereinafter, the compensation element 102calculates the disturbance compensation value Rcyc_cin for the cam phasecontrol according to the target cam phase Cain_cmd, a count C_crk of acrank angle counter, the valve lift Liftin, and the engine speed NE. Itshould be noted that the crank angle counter is an up counter forcounting the crank angle, and as described hereinafter, the count C_crkis incremented by a value of 10 in synchronism with generation of eachpulse of the CRK signal, and reset to a value of 0 when it has reached avalue of 720.

The disturbance compensation value Rcyc_cin for the cam phase control isprovided for compensating for a periodic disturbance which is expectedto occur periodically in accordance with rotation of the intake camshaft5, i.e. rotation of the intake cam 6 during operation of the engine 3.In the following, a description will be given of the periodicdisturbance, -and a method of calculating the disturbance compensationvalue Rcyc_cin for compensating for the periodic disturbance. First, forease of understanding, the periodic disturbance and the method ofcalculating the disturbance compensation value Rcyc_cin are describedwith reference to FIG. 12A to FIG. 17 by taking a case in which theperiodic disturbance occurs in one cylinder 3 a (in other words, a casein which the periodic disturbance occurs in a single-cylinder engine) asan example. Referring to FIG. 12A, in a state where the intake cam 6rotates in a direction indicated by an arrow “Y1” to actuate the intakevalve 4 in the valve-opening direction, the intake cam 6 is subjected toa disturbance acting as a rotation moment in a direction indicated by anarrow “Y2” due to the reaction force of the valve spring 4 e of theintake valve 4.

On the other hand, as shown in FIG. 12B, in a state where the intake cam6 actuates the intake valve 4 in the valve-closing direction, the intakecam 6 is subjected to a disturbance acting as a rotation moment in adirection indicated by an arrow “Y3” due to the urging force of thevalve spring 4 e of the intake valve 4. The disturbances described aboveperiodically occur along with rotation of the intake camshaft 5, and anamplitude of the disturbances also periodically changes. Thereforehereinafter, the disturbances are referred to as “the periodicdisturbance”.

Now, assuming that the intake cam 6 is subjected to the periodicdisturbance described above during feedback control performed so as tocause the cam phase Cain to converge to the target cam phase Cain_cmd,although the target cam phase Cain_cmd is held constant, the cam phaseCain deviates toward the retarded side during a time period over whichthe intake valve 4 is actuated in the valve-opening direction by theintake cam 6, and deviates toward the advanced side during a time periodover which the intake valve 4 is actuated in the valve-closingdirection, as shown in FIG. 13.

When the above deviations of the cam phase Cain occur, the valve timingof the intake valve 4 is varied compared with the case where thevariable cam phase mechanism 70 is not provided. More specifically, asshown in FIGS. 14 and 15, the valve lift curves of the intake valve 4exhibited when the engine 3 is provided with the variable cam phasemechanism 70 (curves indicated by solid lines in FIGS. 14 and 15) showthat the valve-opening time period of the intake valve 4 is shorter thanwhen the engine 3 is not provided with the variable cam phase mechanism70 (curves indicated by broken lines in the figures), so that the amountof intake air is changed to change torque generated by the engine 3,which can make the combustion state of the engine 3 unstable.

To avoid the above inconveniences, it is contemplated, for example, thatthe cam profile of the intake cam 6 is modified in advance. However, asis clear from comparison of the valve lift curves in FIGS. 14 and 15,when the engine 3 includes the variable valve lift mechanism 50, thedegree of change in the valve timing of the intake valve 4, caused whenthe valve lift Liftin is controlled to a predetermined value on a highlift side (which is indicated by the valve lift curve in FIG. 14), andthe degree of change in the valve timing of the intake valve 4, causedwhen the valve lift Liftin is controlled to a predetermined value on alow lift side (which is indicated by the valve lift curve in FIG. 15)are different from each other. Therefore, as in the present embodiment,when the engine 3 includes both of the variable cam phase mechanism 70and the variable valve lift mechanism 50, it is difficult to avoid theinfluence of the periodic disturbance by changing the cam profile of theintake cam 6.

In the present embodiment, to avoid the above influence of the periodicdisturbance on the variable cam phase mechanism 70, the value of theperiodic disturbance applied to the variable cam phase mechanism 70 ispredicted, and a value corresponding to a value obtained by invertingthe sign of the predicted value is calculated as the disturbancecompensation value Rcyc_cin for the cam phase control. Morespecifically, the disturbance compensation value Rcyc_cin for the camphase control is calculated by searching a disturbance compensationvalue map according to the valve lift Liftin, the count C_crk of thecrank angle counter, and the target cam phase Cain_cmd, to therebydetermine a map value Rcyc_bs_cin, and then correcting the map valueRcyc_bs_cin according to the engine speed NE.

As the disturbance compensation value map is used a map which contains amap value Rcyc bs cin for use in Cain_cmd=Cainrt&Liftin=Liftinmax,indicated by a solid line in FIG. 16, a map value Rcyc_bs_cin for use inCain_cmd=Cainrt&Liftin=Liftinmin, indicated by a solid line in FIG. 17,and a plurality of map values Rcyc_bs_cin (not shown) for use ininterpolation in a case where Cain_cmd =Cainrt holds and the valve liftLiftin is between the maximum value Liftinmax and the minimum valueLiftinmin, and set in a manner corresponding to values of Liftin at aplurality of stages, respectively.

In searching the above disturbance compensation value map, when thetarget cam phase Cain_cmd is a value advanced with respect to the mostretarded value Cainrt, the repetition period of occurrence of theperiodic disturbance deviates toward the advanced side (left-hand sideas viewed in FIGS. 16 and 17), so that it is necessary to correct thedisturbance compensation value accordingly e.g. to values indicated bytwo-dot chain lines in FIGS. 16 and 17. Therefore, when the disturbancecompensation value map is searched according to the present embodiment,the count C_crk of the crank angle counter is corrected by taking thedegree of advance of the target cam phase Cain_cmd with respect to themost retarded value Cainrt into account. Then, two map valuesRcyc_bs_cin closer to the present valve lift Liftin are selected fromthe above described map values Rcyc_bs_cin according to the count C_crkcorrected as above and the valve lift Liftin, and the map valueRcyc_bs_cin of the disturbance compensation value for the cam phasecontrol is calculated by interpolation of the two selected values.Furthermore, the map value Rcyc_bs_cin calculated as above is correctedaccording to the engine speed NE, as will be described in detailhereinafter, to thereby determine the disturbance compensation valueRcyc_cin for the cam phase control.

It can be contemplated to calculate the disturbance compensation valueRcyc_cin for the cam phase control, for compensating for the periodicdisturbance generated in the one cylinder 3 a, as described above.However, the engine 3 of the present embodiment is a four-cylinderengine, and hence the periodic disturbance occurs four times in total ineach of the four cylinders 3 a in one control cycle. Moreover, theperiodic disturbances occur in an overlapping manner due to the phasedifference therebetween. Therefore, in the present embodiment, tocompensate for such periodic disturbances, in place of the abovedisturbance compensation value map, a disturbance compensation value mapis used which contains a map value Rcyc_bs_cin for use inCain_cmd=Cainrt&Liftin=Liftinmax shown in FIG. 18, a map valueRcyc_bs_cin for use in Cain_cmd=Cainrt&Liftin=Liftinmin shown in FIG.19, and a plurality of map values Rcyc_bs_cin (not shown) for use ininterpolation in a case where Cain_cmd=Cainrt holds, and at the sametime the valve lift Liftin is between the maximum value Liftinmax andthe minimum value Liftinmin, and set in a manner corresponding to valuesof Liftin at a plurality of stages, respectively.

As is clear from FIGS. 18 and 19, in this disturbance compensation valuemap, the map value Rcyc_bs_cin of the disturbance compensation value forthe cam phase control is set as a value corresponding to the count C_crkof the crank angle counter, according to the results of prediction ofthe periodic disturbance. That is, the map value Rcyc_bs_cin is set intime series order according to the results of prediction of the periodicdisturbance. Further, the repetition period of calculation of the mapvalue Rcyc_bs_cin is set to a time period over which the crankshaft 3 drotates through 180 degrees. This is because for the aforementionedreason, the repetition period of occurrence of the periodic disturbanceapplied to the variable cam phase mechanism 70 corresponds to the timeperiod over which the crankshaft 3 d rotates through 180 degrees. Itshould be noted that the above disturbance compensation value map isstored in the ROM 2 c in advance.

Further, the disturbance compensation value map is searched by the samemethod, as described above. More specifically, the count C_crk of thecrank angle counter is corrected by taking the degree of advance of thetarget cam phase Cain_cmd with respect to the most retarded value Cainrtinto account. Then, two map values Rcyc_bs_cin closer to the presentvalve lift Liftin are selected from the above map values Rcyc_bs_cinaccording to the corrected count C_crk of the crank angle counter andthe valve lift Liftin, and the map value Rcyc_bs_cin (disturbancecompensation value) of the disturbance compensation value for the camphase control is calculated by interpolation of the two selected values.Furthermore, the map value Rcyc_bs_cin calculated as above is correctedaccording to the engine speed NE, as will be described in detailhereinafter, to thereby calculate the disturbance compensation valueRcyc_cin for the cam phase control. Thus, the disturbance compensationvalue Rcyc_cin for the cam phase control is calculated as a valuecorresponding to a value obtained by inverting the sign of a predictedvalue of the periodic disturbance. It should be noted that as describedhereinafter, the calculation of the disturbance compensation valueRcyc_cin for the cam phase control is performed in timing synchronouswith generation of each pulse of the CRK signal.

Next, a description will be given of the aforementionedtwo-degree-of-freedom SLD controller 103. The two-degree-of-freedom SLDcontroller 103 calculates the SLD control input Rsld for the cam phasecontrol according to the target cam phase Cain_cmd and the cam phaseCain with a target value filter-type two-degree-of-freedom sliding modecontrol algorithm [equations (1) to (8) shown in FIG. 20].

In the above equations (1) to (8), discrete data with a symbol (k)indicates that it is data sampled (or calculated) in synchronism with apredetermined control period ΔT (e.g. 5 msec in the present embodiment).The symbol k indicates a position in the sequence of sampling cycles ofrespective discrete data. For example, the symbol k indicates thatdiscrete data therewith is a value sampled in the current controltiming, and a symbol k-1 indicates that discrete data therewith is avalue sampled in the immediately preceding control timing. This appliesto the following discrete data. It should be noted that in the followingdescription, the symbol k and the like provided for the discrete dataare omitted as deemed appropriate.

In the above control algorithm, first, a filtered value Cain_cmd_f ofthe target cam phase is calculated with a first-order lag filteralgorithm expressed by the equation (1). In the equation (1), POLE_frepresents a target value filter-setting parameter, and is set to avalue which satisfies the relationship of −1<POLE_f<0.

Then, the SLD control input Rsld for the cam phase control is calculatedwith a sliding mode algorithm expressed by the equations (2) to (8).More specifically, as expressed by the equation (2), the SLD controlinput Rsld for the cam phase control is calculated as a total sum of anequivalent control input Req, a reaching law input Rrch, an adaptive lawinput Radp, and a nonlinear input Rnl. The equivalent control input Reqis calculated by the equation (3). In the equation (3), a1, a2, b1, andb2 represent model parameters of a model, described hereinafter, and areset to predetermined values. Further, in the equation (3), POLErepresents a switching function-setting parameter, and is set to a valuewhich satisfies the relationship of −1<POLE_f<POLE<0.

Further, the reaching law input Rrch is calculated by the equation (4).In the equation (4), Krch represents a predetermined reaching law gain,and σs represents a switching function defined by the equation (7).

Furthermore, the adaptive law input Radp is calculated by the equation(5). In the equation (5), Kadp represents a predetermined adaptive lawgain. In the meantime, the nonlinear input Rnl is calculated by theequation (6). In the equation (6), Knl represents a predeterminednonlinear gain, and sgn(σs) represents a sign function which has a valueof sgn(σs)=1 when σs≧0 holds, and a value of sgn(σs)=−1 when σs<0 holds(the sign function may be set to a value of sgn(σs)=0 when σs=0 holds).

It should be noted that the above equations (1) to (8) are derived asfollows: A controlled object is defined as a system to which is inputtedthe SLD control input Rsld for the cam phase control and from which isoutputted the cam phase Cain, and modeled into a discrete-time systemmodel, whereby an equation (9) shown in FIG. 20 is obtained. When atarget value filter-type two-degree-of-freedom sliding mode controltheory is applied based on a model expressed by the equation (9) suchthat the cam phase Cain converges to the target cam phase Cain_cmd, theaforementioned equations (1) to (8) are derived.

On the other hand, the above described addition element 104 calculatesthe reference input Rsld_f for the cam phase control as the sum of thedisturbance compensation value Rcyc_cin for the cam phase control andthe SLD control input Rsld for the cam phase control, calculated asabove, as expressed by an equation (10) in FIG. 21.

Next, a description will be given of the aforementioned DSM controller105. The DSM controller 105 calculates the phase control input Ucainwith a control algorithm based on a ΔΣ modulation algorithm, expressedby equations (11) to (16) in FIG. 21. It should be noted that to thecontrol algorithm expressed by the equations (11) to (16) is applied acontrol algorithm which the present assignee has already proposed inJapanese Patent Application No. 2003-293009.

In the equation (11) in FIG. 21, Lim(Rsld_f) represents a limited valueobtained by performing a limiting process on the reference input Rsld_ffor the cam phase control, and is calculated specifically as a valueobtained by limiting the reference input Rsld_f for the cam phasecontrol within a range defined by a predetermined lower limit value Rminand a predetermined upper limit value Rmax. More specifically, whenRsld_f<Rmin, Lim(Rsld_f)=Rmin holds, when Rmin≦Rsld_f<Rmax,Lim(Rsld_f)=Rsld_f holds, and when Rsld_f>Rmax, Lim(Rsld_f)=Rmax holds.The upper limit value Rmax and the lower limit value Rmin are set topredetermined positive and negative values whose absolute values areequal to each other.

Further, in the equation (12), r2 and udsm_oft represent a limited valuedeviation and a predetermined offset value, respectively. Further, inthe equation (13), 6 represents a difference signal value, and iscalculated as the difference between the limited value deviation r2 andthe immediately preceding value of a modulation output u, as expressedby the equation (13).

On the other hand, in the equation (14), a represents a differenceintegral value, which is an integral value of the difference signalvalue 6, and is calculated as the sum of the immediately preceding valuethereof and the difference signal value. Further, in the equation (15),fnl(σ) represents a nonlinear function. The value of fnl(σ) is set suchthat when σ≧0, fnl(σ)=R holds, and when σ<0, fnl(σ)=−R holds (fnl(σ) maybe set such that when σ=0, fnl(σ)=0 holds). Further, the value R is setto a value which always satisfies the relationship of R>|r2|.

With the above control algorithm, the DSM controller 105 of the controlsystem according to the present embodiment calculates the phase controlinput Ucain as a value which is frequently inverted between apredetermined upper limit value and a predetermined lower limit value,whereby it is possible to enhance the control accuracy of the cam phasecontrol.

Next, a description will be given of the aforementioned valve liftcontroller 110. Referring to FIG. 22, the valve lift controller 110includes a target valve lift-calculating section 111, a compensationelement 112, a two-degree-of-freedom SLD controller 113, an additionelement 114, and a DSM controller 115, all of which are implemented bythe ECU 2.

As will be described hereinafter, the valve lift controller 110calculates the lift control input Uliftin, which is inputted to thevariable valve lift mechanism 50, whereby the valve lift Liftin iscontrolled to the target valve lift Liftin cmd.

First, the target valve lift-calculating section 111 (targetvalue-setting means, target valve lift-setting means) calculates thetarget valve lift Liftin_cmd (target value, valve lift parameter) bysearching a map (see FIG. 34), described hereinafter, according to theengine speed NE and the accelerator pedal opening AP.

Further, the compensation element 112 (disturbance compensationvalue-storing means, disturbance compensation value-selecting means)calculates a disturbance compensation value Rcyc_lin, as describedhereinafter. Similarly to the above described disturbance compensationvalue Rcyc_cin for the cam phase control, the disturbance compensationvalue Rcyc_lin is for compensating for the influence of the periodicdisturbance occurring along with rotation of the intake cam 6 duringoperation of the engine 3. More specifically, when such a periodicdisturbance is applied to the variable valve lift mechanism 50, theintake air amount is changed due to changes in the valve lift Liftin, sothat to avoid such changes in the intake air amount, the value of theperiodic disturbance applied to the variable valve lift mechanism 50 ispredicted, and a value corresponding to a value obtained by invertingthe sign of the predicted value is calculated as the disturbancecompensation value Rcyc_lin for the valve lift control.

More specifically, the disturbance compensation value Rcyc_lin for thevalve lift control is calculated by the same method as the method ofcalculating the compensation element 102. First, a map value Rcyc_bs_lin(disturbance compensation value) is calculated by searching adisturbance compensation value map according to the cam phase Cain, thecount C_crk, and the target valve lift Liftin_cmd.

The compensation element 112 uses, as the above disturbance compensationvalue map, a map which contains a map value Rcyc_bs_lin for use inLiftin_cmd=Liftinmax&Cain=Cainrt shown in FIG. 23, a map valueRcyc_bs_lin for use in Liftin_cmd=Liftinmin&Cain=Cainrt shown in FIG.24, and a plurality of map values Rcyc_bs_lin (not shown) for use ininterpolation in a case where Cain=Cainrt holds and at the same time thetarget valve lift Liftin_cmd is between the maximum value Liftinmax andthe minimum value Liftinmin, and set in a manner corresponding to valuesof Liftin cmd at a plurality of stages, respectively. It should be notedthat this disturbance compensation value map is stored in the ROM 2 c inadvance.

When the above disturbance compensation value map is searched, the countC_crk of the crank angle counter is corrected according to the degree ofadvance of the cam phase Cain with respect to the most retarded valueCainrt, and according to the corrected count C_crk and the target valvelift Liftin_cmd, two map values closer to the present target valve liftLiftin_cmd are selected from the above map values Rcyc_bs_lin, and themap value Rcyc_bs_lin of the disturbance compensation value for thevalue lift control is calculated by interpolation of the two selectedvalues.

Then, the map value Rcyc_bs_lin calculated as above is correctedaccording to the engine speed NE, as described hereinafter, whereby thedisturbance compensation value Rcyc_lin (corrected disturbancecompensation value) for the valve lift control is calculated. It shouldbe noted that as described hereinafter, the calculation of thedisturbance compensation value Rcyc_lin for the valve lift control isperformed in the timing synchronous with generation of each pulse of theCRK signal.

On the other hand, the two-degree-of-freedom SLD controller 113 (controlinput-calculating means) calculates an SLD control input Rsld′ for thevalve lift control according to the target valve lift Liftin_cmd and thevalve lift Liftin, with a target value filter-type two-degree-of-freedomsliding mode control algorithm similar to the aforementioned controlalgorithm [equations (1) to (8)] for the two-degree-of-freedom SLDcontroller 103.

More specifically, in the two-degree-of-freedom SLD controller 113, theSLD control input Rsld′ for the valve lift control is calculated with analgorithm defined such that in the equations (1) to (8) appearing inFIG. 20, the cam phase Cain, the target cam phase Cain_cmd, and the SLDcontrol input Rsld for the cam phase control are replaced by the valvelift Liftin, the target valve lift Liftin_cmd, and the SLD control inputRsld′ for the valve lift control, respectively, and the variables, theparameters, and the predetermined set values are replaced by respectivecorresponding values for the valve lift control.

Further, the aforementioned addition element 114 (controlinput-calculating means) calculates a reference input Rsld_f′ (controlinput) for the valve lift control as the sum of the disturbancecompensation value Rcyc_lin for the valve lift control, calculated bythe compensation element 112, and the SLD control input Rsld′ for thevalve lift control, calculated by the two-degree-of-freedom SLDcontroller 113.

Furthermore, the aforementioned DSM controller 115 (controlinput-calculating means) calculates the lift control input Uliftinaccording to the reference input Rsld_f′ for the valve lift control,with a control algorithm similar to the above described controlalgorithm [equations (11) to (16)] for the DSM controller 105. Morespecifically, in the DSM controller 115, the lift control input Uliftinis calculated with an algorithm defined such that in the equations (11)to (16) appearing in FIG. 21, the reference input Rsld_f for the camphase control and the phase control input Ucain are replaced by thereference input Rsld_f′ for the valve lift control and the lift controlinput Uliftin, respectively, and the functions and the predetermined setvalues are replaced by respective corresponding values for the valvelift control.

Next, a description will be given of the aforementioned compressionratio controller 120. As shown in FIG. 25, the compression ratiocontroller 120 includes a target compression ratio-calculating section121, a compensation element 122, a two-degree-of-freedom SLD controller123, an addition element 124, and a DSM controller 125, all of which areimplemented by the ECU 2.

The compression ratio controller 120 calculates, as describedhereinafter, the compression ratio control input Ucr, which is inputtedto the variable compression ratio mechanism 80, whereby the compressionratio Cr is controlled to a target compression ratio Cr_cmd.

First, the target compression ratio-calculating section 121 (targetvalue-setting means, target compression ratio-setting means) calculatesthe target compression ratio Cr_cmd (compression ratio parameter) bysearching a map, described hereinafter (see FIG. 35), according to theengine speed NE and the accelerator pedal opening AP.

Further, the compensation element 122 (disturbance compensationvalue-storing means, disturbance compensation value-selecting means)calculates, as described hereinafter, a disturbance compensation valueRcyc_cr for the compression ratio control. The disturbance compensationvalue Rcyc_cr for the compression ratio control is provided forcompensating for the influence of a periodic disturbance caused bycombustion pressure during operation of the engine 3. More specifically,when such a periodic disturbance is applied to the variable compressionratio mechanism 80, the compression ratio Cr is changed to therebydegrade compatibility between the same and the ignition timing set bythe ignition timing control, which can cause occurrence of knocking anddegradation of combustion efficiency. Therefore, in the compensationelement 122, to avoid such a change in the compression ratio, the valueof the periodic disturbance applied to the variable compression ratiomechanism 80 is predicted, and a value obtained by inverting the sign ofthe predicted value is calculated as the disturbance compensation valueRcyc_cr for the compression ratio control.

More specifically, the disturbance compensation value Rcyc_cr for thecompression ratio control is determined as follows: First, a map valueRcyc_bs cr (disturbance compensation value) is calculated by searching adisturbance compensation value map according to the compression ratio Crand the count C_crk of the crank angle counter.

The compensation element 122 uses, as the disturbance compensation valuemap, a map which contains a map value Rcyc_bs_cr for use inCr_cmd=Crmax, indicated by a solid line in FIG. 26, a map valueRcyc_bs_cr for use in Cr_cmd=Crmin, indicated by a broken line in FIG.26, and a plurality of map values Rcyc_bs_cr (not shown) for use ininterpolation in a case where the target compression ratio Cr_cmd isbetween the maximum value Crmax and the minimum value Crmin, and set ina manner corresponding to values of Cr_cmd at a plurality of stages,respectively. This disturbance compensation value map is stored in theROM 2 c in advance. It should be noted that although in the presentembodiment, the above disturbance compensation value map is employed dueto the geometry of the variable compression ratio mechanism 80, this isnot limitative, but a disturbance compensation value map may be used inwhich the relationship between a value for Crmax and a value for Crminis set reversely, depending on the geometry of the variable compressionratio mechanism.

Further, two map values closer to the present target compression ratioCr_cmd are selected from the above map values, and the map valueRcyc_bs_cr of the disturbance compensation value for the compressionratio control is calculated by interpolation of the two selected values.

Then, the map value Rcyc_bs_cr calculated as above is correctedaccording to the cam phase Cain, the valve lift Liftin, and the enginespeed NE, as described hereinafter, to thereby calculate the disturbancecompensation value Rcyc_cr for the compression ratio control. It shouldbe noted that as described hereinafter, the calculation of thedisturbance compensation value Rcyc_cr for the compression ratio controlis performed in timing synchronous with generation of each pulse of theCRK signal.

On the other hand, the two-degree-of-freedom SLD controller 123 (controlinput-calculating means) calculates an SLD control input Rsld″ for thecompression ratio control according to the target compression ratioCr_cmd and the compression ratio Cr, with a target value filter-typetwo-degree-of-freedom sliding mode control algorithm similar to theaforementioned control algorithm [equations (1) to (8)] for thetwo-degree-of-freedom SLD controller 103.

More specifically, in the two-degree-of-freedom SLD controller 123, theSLD control input Rsld″ for the compression ratio control is calculatedwith an algorithm defined such that in the equations (1) to (8)appearing in FIG. 20, the cam phase Cain, the target cam phase Cain_cmd,and the SLD control input Rsld for the cam phase control are replaced bythe compression ratio Cr, the target compression ratio Cr_cmd, and theSLD control input Rsld″ for the compression ratio control, respectively,and the variables, the parameters, and the predetermined set values arereplaced by respective corresponding values for the compression ratiocontrol.

Further, the aforementioned addition element 124 (controlinput-calculating means) calculates a reference input Rsld f″ (controlinput) for the compression ratio control as the sum of the disturbancecompensation value Rcyc_cr for the compression ratio control, calculatedby the compensation element 122, and the SLD control input Rsld″ for thecompression ratio control, calculated by the two-degree-of-freedom SLDcontroller 123.

Furthermore, the aforementioned DSM controller (controlinput-calculating means) 125 calculates the compression ratio controlinput Ucr according to the reference input Rsld f″ for the compressionratio control, with a control algorithm similar to the above describedcontrol algorithm [equations (11) to (16)] for the DSM controller 105.More specifically, in the DSM controller 125, the compression ratiocontrol input Ucr is calculated with an algorithm defined such that inthe equations (11) to (16) appearing in FIG. 21, the reference inputRsld_f for the cam phase control and the phase control input Ucain arereplaced by the reference input Rsld f″ for the compression ratiocontrol and the compression ratio control input Ucr, respectively, andthe functions and the predetermined set values are replaced byrespective corresponding values for the compression ratio control.

Next, a description will be given of control processes carried out bythe ECU 2. First, a process for calculating the three disturbancecompensation values Rcyc_cin, Rcyc_lin, and Rcyc_cr will be described indetail with reference to FIG. 27 to FIG. 31. This processes correspondsto the above described calculation processes by the compensationelements 102, 112, and 122, and is carried out in the timing synchronouswith generation of each pulse of the CRK signal, after a time point whenthe crankshaft 3 d has reached a predetermined crank angle position(e.g. crank angle position in which a piston 3 b in a predeterminedassociated cylinder 3 a is in the TDC position) after the IG·SW 27 hasbeen turned on. More specifically, the repetition period of execution ofthe process corresponds to the repetition period of generation of theCRK signal, and as described above, the repetition period of occurrenceof the periodic disturbance corresponds to the time period over whichthe crankshaft 3 d rotates through 180 degrees, and hence the repetitionperiod of execution of the process corresponds to one eighteenth of therepetition period of occurrence of the periodic disturbance.

Referring to FIG. 27, in the above process, first, in a step 1 (shown asS1 in abbreviated form in FIG. 27; the following steps are also shown inabbreviated form), it is determined whether or not a calculation flagF_CAL is equal to 1. The calculation flag F_CAL is set to 0 when theIG·SW 27 is turned on. Therefore, when the current loop is a first one,the answer to the question of the step 1 is negative (NO), and theprocess proceeds to a step 2, wherein calculation flag F_CAL is set to1. Thus, the answer to the question of the step 1 becomes affirmative(YES) in the following loops.

Then, in a step 3, the count C_crk of the crank angle counter is set toa value of 0, followed by the process proceeding to a step 6, referredto hereinafter.

On the other hand, if the answer to the question of the step 1 isaffirmative (YES), the process proceeds to a step 4, wherein the countC_crk of the crank angle counter is incremented by a value of 10. Then,in a step 5, it is determined whether or not the count C_crk of thecrank angle counter is equal to 720. If the answer to this question isnegative (NO), the process proceeds to the step 6, referred tohereinafter. On the other hand, if the answer to this question isaffirmative (YES), the process proceeds to the above described step 3,wherein the count C_crk of the crank angle counter is set to 0, followedby the process proceeding to the step 6.

In the step 6 following the step 3 or the step 5, the map valueRcyc_bs_cin of the disturbance compensation value for the cam phasecontrol is calculated. More specifically, as described hereinbefore, themap value Rcyc_bs_cin of the disturbance compensation value for the camphase control is calculated by searching the aforementioned disturbancecompensation value map (FIGS. 18 and 19) for the cam phase control,according to the target cam phase Cain_cmd, the count C_crk of the crankangle counter, and the valve lift Liftin.

Then, the process proceeds to a step 7, wherein a correction coefficientKrcyc_cin for the cam phase control is calculated by searching a tablein FIG. 28 according to the engine speed NE. As shown in FIG. 28, inthis table, the correction coefficient Krcyc_cin is set to a largervalue as the engine speed NE is lower. This is to compensate for anincrease in the periodic displacement of the intake cam 6, because thefrequency of the periodic disturbance decreases in a low-engine speedregion, causing an increase in responding gain of a cam phase controlsystem to an external force and hence causing the increase in theperiodic displacement of the intake cam 6.

Further, in the above table, the correction coefficient Krcyc_cin is setto a value of 0 within a range where the engine speed NE is not lowerthan a predetermined rotational speed NEREF1 (e.g. 4000 rpm). This isbecause in a high rotational speed region, the solenoid valve mechanism74 as an actuator does not have sufficient responsiveness, which makesit difficult to accurately compensate for the periodic disturbance, andmoreover although the frequency of the periodic disturbance becomeshigh, the response characteristics (low-pass characteristics) of thevariable cam phase mechanism 70 prevents the mechanism 70 from beingadversely affected by the periodic disturbance having the highfrequency.

In a step 8 following the step 7, the disturbance compensation valueRcyc_cin for the cam phase control is set to the product of the mapvalue Rcyc_bs_cin and the correction coefficient Krcyc_cin calculated inthe respective steps 6 and 7, and stored in the RAM 2 b.

Then, in a step 9, the map value Rcyc_bs_lin of the disturbancecompensation value for the valve lift control is calculated. Morespecifically, as described above, the map value Rcyc_bs_lin of thedisturbance compensation value for the valve lift control is calculatedby searching the aforementioned disturbance compensation value map(FIGS. 23 and 24) for the valve lift control, according to the targetvalve lift Liftin_cmd, the cam phase Cain, and the count C_crk of thecrank angle counter.

Next, the process proceeds to a step 10, wherein a correctioncoefficient Krcyc_lin for the valve lift control is calculated bysearching a table shown in FIG. 29 according to the engine speed NE. Asshown in FIG. 29, in this table, the correction coefficient Krcyc_lin isset to a larger value as the engine speed NE is lower. This is tocompensate for an increase in the periodic deviation of the valve liftLiftin, because the frequency of the periodic disturbance decreases inthe low-engine speed region, causing an increase in responding gain of avalve lift control system to an external force, and hence causing theincrease in the periodic deviation of the value lift Liftin.

Further, in the above table, the correction coefficient Krcyc_lin is setto a value of 0 within a range where the engine speed NE is not lowerthan a predetermined rotational speed NEREF2 (e.g. 5000 rpm). This isbecause in the high rotational speed region, the lift actuator 60 doesnot have sufficient responsiveness, which makes it difficult toaccurately compensate for the periodic disturbance, and moreoveralthough the frequency of the periodic disturbance becomes high, theresponse characteristics (low-pass characteristics) of the variablevalve lift mechanism 50 prevents the mechanism 50 from being adverselyaffected by the periodic disturbance having the high frequency.

In a step 11 following the step 10, the disturbance compensation valueRcyc_lin for the valve lift control is set to the product of the mapvalue Rcyc_bs_lin and the correction coefficient Krcyc_lin calculated inthe respective steps 9 and 10.

Then, the process proceeds to a step 12, wherein the map valueRcyc_bs_cr of the disturbance compensation value for the compressionratio control is calculated. More specifically, as described above, themap value Rcyc_bs_cr is calculated by searching the aforementioneddisturbance compensation value map (FIG. 26) for the compression ratiocontrol, according to the count C_crk of the crank angle counter and thetarget compression ratio Cr_cmd.

Next, in a step 13, a first correction coefficient Krcyc_cr1 for thecompression ratio control is calculated by searching a map shown in FIG.30 according to the cam phase Cain and the valve lift Liftin. It shouldbe noted that predetermined values Liftin1 to Liftin3 of the valve liftshown in FIG. 30 are set such that the relationship ofLiftin1>Liftin2>Liftin3 holds therebetween.

As shown in FIG. 30, in this map, the first correction coefficientKrcyc_cr1 is set to a smaller value, as the value of the cam phase Cainis more advanced, or as the valve lift Liftin is smaller. This isbecause as the value of the cam phase Cain is more advanced, theinternal EGR amount increases to thereby lower the combustiontemperature and the combustion pressure of the mixture, which makes theamplitude of the periodic disturbance smaller, and as the value of thevalve lift Liftin is smaller, the intake air amount decreases to lowerthe combustion pressure, which makes the amplitude of the periodicdisturbance smaller.

Then, in a step 14, a second correction coefficient Krcyc_cr2 for thecompression ratio control is calculated by searching a table shown inFIG. 31 according to the engine speed NE. As shown in FIG. 31, in thistable, the second correction coefficient Krcyc_cr2 is set such that itexhibits a maximum value when NE=NEREF4 (<NEREF3) holds, in a regionwhere the engine speed NE is lower than a predetermined rotational speedNEREF3 (e.g. 3000 rpm). In the low-engine speed region, the amplitude ofthe periodic disturbance exhibits a maximum value when NE=NEREF4 holds,due to the influence of the inertial mass, and the table is configuredas described above, for compensation of this.

Further, in the above table, the second correction coefficient Krcyc_cr2is set to a value of 0 within a range where NE≧NEREF3 holds. This isbecause in the high rotational speed region, the compression ratioactuator 87 does not have sufficient responsiveness, which makes itdifficult to accurately compensate for the periodic disturbance, andmoreover although the frequency of the periodic disturbance caused bythe combustion pressure become high, the response characteristics(low-pass characteristics) of the variable compression ratio mechanism80 prevents the mechanism 80 from being adversely affected by theperiodic disturbance having the high frequency.

In a step 15 following the step 14, the disturbance compensation valueRcyc_cr for the compression ratio control is set to the product of themap value Rcyc_bs_lin and the first and second correction coefficientsKrcyc_cr1 and Krcyc_cr2 calculated in the respective steps 12 to 14,followed by terminating the present process.

Next, a process for calculating the aforementioned three control inputsUcain, Uliftin, and Ucr will be described with reference to FIG. 32.This process is executed at the predetermined control period AT (5 msecin the present embodiment) according to settings of a program timer.

As shown in FIG. 32, in the above process, first, in a step 20, it isdetermined whether or not a variable mechanism OK flag F_VDOK is equalto 1. The variable mechanism OK flag F_VDOK is set to 1, when thevariable cam phase mechanism 70, the variable valve lift mechanism 50,and the variable compression ratio mechanism 80 are all normal, andotherwise set to 0.

If the answer to the question of the step 20 is negative (NO), i.e. ifat least one of the three variable mechanisms 50, 70, and 80 is faulty,the process proceeds to a step 32, wherein the phase control inputUcain, the lift control input Uliftin, and the compression ratio controlinput Ucr are all set to a value of 0, followed by terminating thepresent process. It should be noted that when all the three controlinputs are set to a value of 0, the cam phase Cain is held at a mostretarded value Cainrt by the variable cam phase mechanism 70, the valvelift Liftin is held at a value suitable for idling or starting of theengine 3 by the variable valve lift mechanism 50, and the compressionratio Cr is held at the minimum value Crmin by the variable compressionratio mechanism 80.

On the other hand, if the answer to the question of the step 20 isaffirmative (YES), i.e. if all the three variable mechanisms 50, 70, and80 are normal, the process proceeds to a step 21, wherein it isdetermined whether or not an engine start flag F_ENGST is equal to 1.The engine start flag F_ENGST is set to 1 when the engine 3 is beingstarted, and set to 0 when the engine 3 has been started. If the answerto the above question is affirmative (YES), i.e. if the engine 3 isbeing started, the process proceeds to a step 22, wherein the target camphase Cain_cmd is set to a predetermined start-time value Cain_cmd_stfor starting of the engine 3.

Then, in steps 23 and 24, the target valve lift Liftin_cmd and thetarget compression ratio Cr_cmd are set to predetermined start-timevalues Liftin_cmd_st and Cr_cmd_st for starting of the engine 3,respectively.

Then, the process proceeds to a step 25, wherein the values of the threedisturbance compensation values Rcyc_cin, Rcyc_lin, and Rcyc_crcurrently stored in the RAM 2b are read in. That is, these values aresampled.

In a step 26 following the step 25, the phase control input Ucain iscalculated, using the calculated target cam phase Cain_cmd, and the readdisturbance compensation value Rcyc_cin for the cam phase control, withthe control algorithms expressed by the above described equations (1) to(8), and (10) to (16).

Next, in a step 27, the lift control input Uliftin is calculated. Asdescribed hereinbefore, the lift control input Uliftin is calculatedwith control algorithms similar to the control algorithms with which thephase control input Ucain is calculated. More specifically, the liftcontrol input Uliftin is calculated, using the calculated target valvelift Liftin_cmd, and the read disturbance compensation value Rcyc_linfor the valve lift control, with control algorithms similar to thecontrol algorithms expressed by the equations (1) to (8), and (10) to(16).

Then, in a step 28, the compression ratio control input Ucr iscalculated. As described hereinbefore, the compression ratio controlinput Ucr as well is calculated with control algorithms similar to thecontrol algorithms with which the phase control input Ucain iscalculated. More specifically, the compression ratio control input Ucris calculated, using the calculated target compression ratio Cr_cmd, andthe read disturbance compensation value Rcyc_cr for the compressionratio control, with control algorithms similar to the control algorithmsexpressed by the equations (1) to (8), and (10) to (16). After that, thepresent process is terminated.

On the other hand, if the answer to the question to the step 21 isnegative (NO), i.e. if the engine 3 has been started, the processproceeds to a step 29, wherein the target cam phase Cain_cmd iscalculated by searching a map shown in FIG. 33 according to the enginespeed NE and the accelerator pedal opening AP. In FIG. 33, predeterminedvalues AP1 to AP3 of the accelerator pedal opening AP are set such thatthe relationship of AP1>AP2>AP3 holds therebetween, and thisrelationship also applies to the following descriptions.

In this map, when AP=AP1 holds, i.e. the load on the engine is high, thetarget cam phase Cain_cmd is set to a more retarded value as the enginespeed NE is higher. Further, when AP=AP2 holds, i.e. the load on theengine is medium, in a low-to-medium engine speed region, the target camphase Cain_cmd is set to a more advanced value as the engine speed NE ishigher, and in a medium-to-high engine speed region, it is set to a moreretarded value as the engine speed NE is higher. Furthermore, also whenAP=AP3 holds, i.e. the load on the engine is low, the target cam phaseCain_cmd is set such that it has the same tendency in value as when theload on the engine is medium. The reason for this will be describedhereinafter.

In a step 30 following the step 29, the target valve lift Liftin_cmd iscalculated by searching a map shown in FIG. 34 according to the enginespeed NE and the accelerator pedal opening AP. In this map, when AP=AP1holds, i.e. the load on the engine is high, the target valve liftLiftin_cmd is set to a larger value as the engine speed NE is higher.Further, when AP=AP2 holds, i.e. the load on the engine is medium, thetarget valve lift Liftin_cmd is set to a larger value as the enginespeed NE is higher, in a low engine speed region, set to substantiallythe same value with respect to the engine speed NE, in a medium enginespeed region and set to a larger value as the engine speed NE is higherin a high engine speed region. Furthermore, also when AP=AP3 holds i.e.the load on the engine is low, the target valve lift Liftin_cmd is setsuch that it has the same tendency in value as when the load on theengine is medium.

The reason why the target valve lift Liftin cmd is set as describedabove, and the target cam phase Cain_cmd is set as described above is asfollows: In the low-load/low-engine speed region, the valve lift Liftinis controlled to the low lift, and at the same time the cam phase Cainis controlled to an advanced value, whereby the Miller cycle is realizedin which the intake valve 4 is closed in earlier timing than in the Ottocycle, to thereby reduce the pumping loss and increase the fluidity ofthe mixture within the cylinders 3 a by lowering the valve lift Liftin,which contributes to increased combustion speed and enhanced combustionefficiency.

Further, in the medium-load/medium-engine speed region, the valve liftLiftin is controlled to the medium lift, and at the same time the camphase Cain is controlled to an advanced value, whereby the valve overlapis increased to increase the internal EGR amount, and the Miller cyclefor earlier closing of the intake valve 4 is realized, to thereby reducethe pumping loss and enhance fuel economy.

Furthermore, in the high-load/high-engine speed region, the valve liftLiftin is controlled to the high lift, and at the same time the camphase Cain is controlled to a retarded value, to thereby increase theintake air amount to increase the engine torque. Additionally, duringexecution of these control operations, the internal EGR amountdecreases, and the intake behavior continues by the inertia force ofintake air at an early stage of the compression stroke, and thereforethe cam phase Cain is controlled to a retarded value to utilize thedecrease in the internal EGR amount and the continuation of the intakebehavior, for enhancement of charging efficiency.

In a step 31 following the step 30, the target compression ratio Cr_cmdis calculated by searching a map shown in FIG. 35 according to theengine speed NE and the accelerator pedal opening AP. In this map, thetarget compression ratio Cr_cmd is set to a smaller value as theaccelerator pedal opening AP is larger, i.e. the load on the engine ishigher or as the engine speed NE is higher. This is because as theengine speed NE is higher, and the accelerator pedal opening AP islarger (i.e. the load on the engine is higher), an optimal value of thecompression ratio for the ignition timing becomes smaller. In otherwords, if the compression ratio Cr is set to a high value when theengine speed NE and the load on the engine are both high, it isnecessary to cause the ignition timing to be retarded so as to preventoccurrence of knocking, which can reduce torque generated by the engine3 (efficiency of the engine 3). To avoid the reduction of the generatedtorque, the map is configured as described above.

Then, as described above, the steps 28 to 28 are carried out tocalculate the three control inputs Ucain, Uliftin, and Ucr, followed byterminating the present process.

As described hereinabove, in the control system 1 according to thepresent embodiment, the three disturbance compensation values Rcyc_cin,Rcyc_lin, and Rcyc_cr are calculated by searching the maps and tables,in the timing synchronous with generation of each pulse of the CRKsignal, as values compensating for a predicted periodic disturbance,obtained by inverting the sign of the periodic disturbance. Further, thethree control inputs Ucain, Uliftin, and Ucr are calculated with theabove-described control algorithms [equations (1) to (8), and (10) to(16)], and the control algorithms similar thereto, according to thethree disturbance compensation values Rcyc_cin, Rcyc_lin, and Rcyc_crcalculated as above, respectively.

Therefore, the cam phase Cain, the valve lift Liftin, and thecompression ratio Cr are controlled in a feedforward manner by thecontrol inputs Ucain, Uliftin, and Ucr calculated as above,respectively, whereby it is possible to compensate for and suppress theinfluence of the periodic disturbance on the cam phase Cain, the valvelift Liftin, and the compression ratio Cr, more quickly than the priorart. As a result, in the cam phase control and the valve lift control,it is possible to avoid a change in the intake air amount, which iscaused by periodic disturbance occurring when the intake valve 4 isopened, thereby making it possible to avoid a change in torque generatedby the engine 3 and ensure a stable combustion state of the engine 3.Further, in the compression ratio control, it is possible to avoid achange in the compression ratio Cr due to the influence of the periodicdisturbance to maintain excellent compatibility between the compressionratio Cr and the ignition timing. This makes it possible to avoidoccurrence of knocking and reduction of combustion efficiency. Thus, thestability and accuracy of control can be improved.

Further, since the target value filter-type two-degree-of-freedomcontrol algorithms are employed for calculating the control inputsUcain, Uliftin, and Ucr, the cam phase Cain, the valve lift Liftin, andthe compression ratio Cr can be caused to converge to the target camphase Cain_cmd, the target valve lift Liftin_cmd, and the targetcompression ratio Cr_cmd in a quick and stable behavior, respectively.For example, even when there occurs a large difference between the camphase Cain and the target cam phase Cain_cmd, it is possible to causethe cam phase Cain to converge to the target cam phase Cain_cmd quicklyand accurately, while avoiding overshooting which might be caused by thedifference.

When the disturbance compensation value Rcyc_cin for the cam phasecontrol is calculated, the map value Rcyc_bs_cin thereof is calculatedaccording to the valve lift Liftin and the target cam phase Cain_cmd,and hence the disturbance compensation value Rcyc_cin can be calculatedas a value which is capable of suitably compensating for not only atleast one of a change in the amplitude of the periodic disturbance and achange in the behavior thereof, caused by a change in the valve liftLiftin, but also a change in the phase of the periodic disturbance,caused by a change in the cam phase Cain. Further, since the correctioncoefficient Krcyc_cin is calculated using the FIG. 28 table, accordingto the engine speed NE, and the map value Rcyc_bs_cin is corrected bythe calculated correction coefficient Krcyc_cin to thereby calculate thedisturbance compensation value Rcyc_cin, a change in the frequency ofthe periodic disturbance, caused by a change in the engine speed NE canbe properly reflected on the disturbance compensation value Rcyc_cin.

Furthermore, the correction coefficient Krcyc_cin is set to a value of 0within the range where the engine speed NE is not lower than thepredetermined rotational speed NEREF1. Therefore, in the high enginespeed region where the variable cam phase mechanism 70 does not havesufficient responsiveness (that is the solenoid valve mechanism 74 as anactuator is low in response), which makes it difficult to accuratelycompensate for the periodic disturbance, compensation for the periodicdisturbance by the disturbance compensation value Rcyc_cin is avoided,whereby it is possible to avoid degradation of controllability.

Further, when the disturbance compensation value Rcyc_lin for the valvelift control is calculated, the map value Rcyc_bs_lin thereof iscalculated according to the target valve lift Liftin_cmd and the camphase Cain, and hence the disturbance compensation value Rcyc_lin can becalculated as a value which is capable of suitably compensating for notonly at least one of a change in the amplitude of the periodicdisturbance and a change in the behavior thereof, caused by a change inthe valve lift Liftin, but also a change in the phase of the periodicdisturbance, caused by a change in the cam phase Cain. Further, sincethe correction coefficient Krcyc_lin is calculated using the FIG. 29table, according to the engine speed NE, and the map value Rcyc_bs_linis corrected by the calculated correction coefficient Krcyc_lin tothereby calculate the disturbance compensation value Rcyc_lin, a changein the frequency of the periodic disturbance, caused by a change in theengine speed NE can be properly reflected on the disturbancecompensation value Rcyc_lin.

Furthermore, the correction coefficient Krcyc_lin is set to a value of 0within the range where the engine speed NE is not lower than thepredetermined rotational speed NEREF2. Therefore, in the high enginespeed region where the variable valve lift mechanism 50 does not havesufficient responsiveness (that is, the lift actuator 60 is low inresponse), which makes it difficult to accurately compensate for theperiodic disturbance, compensation for the periodic disturbance by thedisturbance compensation value Rcyc_lin is avoided, whereby it ispossible to avoid degradation of the controllability.

Further, when the disturbance compensation value Rcyc_cr for thecompression ratio control is calculated, the map value Rcyc_bs_crthereof is calculated according to the target compression ratio Cr_cmd,and hence the disturbance compensation value Rcyc_cr can be calculatedas a value which is capable of suitably compensating for a change in theamplitude of the periodic disturbance, caused by a change in thecompression ratio Cr. Furthermore, the first correction coefficientKrcyc_cr1 is calculated using the FIG. 30 map, according to the camphase Cain and the valve lift Liftin, and the map value Rcyc_bs_cr iscorrected by the first correction coefficient Krcyc_cr1 to therebycalculate the disturbance compensation value Rcyc_cr. This makes itpossible to calculate the disturbance compensation value Rcyc_cr as avalue which is capable of suitably compensating for a change in theamplitude of the periodic disturbance, caused by changes in the valvelift Liftin and the cam phase Cain.

Furthermore, the second correction coefficient Krcyc_cr2 is calculatedusing the FIG. 31 table, according to the engine speed NE, and the mapvalue Rcyc_bs_cr is corrected by the second correction coefficientKrcyc_cr2 to thereby calculate the disturbance compensation valueRcyc_cr. This makes it possible to cause a change in the frequency ofthe periodic disturbance, caused by a change in the engine speed NE, tobe properly reflected on the disturbance compensation value Rcyc_cr.Further, the second correction coefficient Krcyc_cr2 is set to a valueof 0 within the range where the engine speed NE is not lower than thepredetermined rotational speed NEREF3. Therefore, in the high rotationalspeed region where the variable compression ratio mechanism 80 does nothave sufficient responsiveness (that is, the compression ratio actuator87 is low in response), which makes it difficult to accuratelycompensate for the periodic disturbance, compensation for the periodicdisturbance by the disturbance compensation value Rcyc_cr can beavoided, whereby it is possible to avoid degradation of controllability.

As described hereinabove, it is possible to markedly improve thestability and the accuracy of control in all of the cam phase control,the valve lift control, and the compression ratio control.

FIG. 36 shows the results of a simulation of cam phase control in whichthe cam phase Cain is controlled using the phase control input Ucaincalculated by the above control method, while holding the target camphase Cain_cmd at a constant value, by taking the cam phase control inonly one cylinder 3 a as an example. As is clear from comparison betweenFIGS. 36 and 13 referred to hereinbefore, according to the controlsystem 1 of the present embodiment, the influence of the periodicdisturbance can be effectively suppressed by using the aforementioneddisturbance compensation value Rcyc_cin for the cam phase control.

Although in the first embodiment, calculation timing (i.e. executiontiming for executing the FIG. 27 process) as selection timing forselecting the three disturbance compensation values Rcyc_cin, Rcyc_lin,and Rcyc_cr is set to timing of generation of each pulse of the CRKsignal, this is not limitative, but the selection timing for selectingthe three disturbance compensation values may be set to timingcorresponding to each rotation of the crankshaft 3 d through apredetermined angle. For example, the selection timing may be set totiming synchronous with generation of each pulse of the CAM signal. Inthis case, in the compensation elements 102, 112, and 122, as the mapsused for calculating the disturbance compensation values Rcyc_cin,Rcyc_lin, and Rcyc_cr, there may be used maps set according to the countof a counter which is incremented by a value corresponding to apredetermined cam angle in synchronism with generation of each pulse ofthe CAM signal in place of the count C_crk of the crank angle counter.

Further, the compensation element 102 may calculate the map valueRcyc_bs_cin of the disturbance compensation value according to thetarget valve lift Liftin_cmd as the valve lift parameter and the camphase Cain as the cam phase parameter, in place of the valve lift Liftinand the target cam phase Cain_cmd, respectively. Further, thecompensation element 112 may also calculate the map value Rcyc_bs_lin ofthe disturbance compensation value according to the valve lift Liftin asthe valve lift parameter and the target cam phase Cain_cmd as the camphase parameter, in place of the target valve lift Liftin and the camphase Cain, respectively.

Similarly, the compensation element 122 may calculate the map valueRcyc_bs_cr of the disturbance compensation value according to thecompression ratio Cr as the compression ratio parameter in place of thetarget compression ratio Cr_cmd, and the first correction coefficientKrcyc_cr1 according to the target valve lift Liftin_cmd as the valvelift parameter and the target cam phase Cain_cmd as the cam phaseparameter, in place of the valve lift Liftin and the target cam phaseCain, respectively.

Further, although the first embodiment is an example in which in thecalculation of the map value Rcyc_bs_cin, there is employed the methodof correcting the count C_crk of the crank angle counter according tothe target cam phase Cain_cmd and searching one kind of disturbancecompensation value map (FIGS. 18 and 19) according to the count C_crk ofthe crank angle counter and the valve lift Liftin, this is notlimitative, but a plurality of kinds of disturbance compensation valuemaps set according to a plurality of values of the target cam phaseCain_cmd, respectively, may be used. For example, a disturbancecompensation value map for use in Cain_cmd=Cainft, one for use inCain_cmd=Cainad, and a plurality of ones set for calculating values ofthe target cam phases Cain_cmd at a plurality of stages therebetween maybe prepared, and two disturbance compensation value maps closer to thepresent target cam phase Cain_cmd may be selected therefrom to calculatethe map value Rcyc_bs_cin by interpolation of map values on the twoselected maps. Similarly, when the map value Rcyc_bs lin of thedisturbance compensation value Rcyc_lin is calculated, a plurality ofdisturbance compensation value maps set according to a plurality ofvalues of the target valve lift Liftin_cmd, respectively, may be used asthe disturbance compensation value maps.

Furthermore, although in the first embodiment, the target valuefilter-type two-degree-of-freedom sliding mode control algorithms areemployed as control algorithms for calculating the reference input Rsldfor the cam phase control, this is not limitative, but any controlalgorithms for calculating the reference input Rsld for the cam phasecontrol may be employed so long as they are control algorithms which arecapable of calculating the reference input Rsld for the cam phasecontrol as a value capable of causing the cam phase Cain to converge tothe target cam phase Cain_cmd. For example, feedback control algorithms,such as PID control algorithms, and response-specifying controlalgorithms, such as back-stepping control algorithms, may be employed.Similarly, feedback control algorithms, such as PI control algorithmsand the PID control algorithms, and the response-specifying controlalgorithms, such as the back-stepping control algorithms, may be used ascontrol algorithms for calculating the reference input Rsld_f′ for thevalve lift control and the reference input Rsld″ for the compressionratio control.

Further, although in the first embodiment, the target value filter-typetwo-degree-of-freedom sliding mode control algorithms are employed asthe response-specifying control algorithms, this is not limitative, butany response-specifying control algorithms may be employed so long asthey are algorithms, such as the back-stepping control algorithms, whichare capable of specifying the convergence rate and the convergingbehavior of the output of a controlled object to a target value.

Further, although in the first embodiment, the DSM controller 105 isemployed for calculating the phase control input Ucain in the cam phasecontroller 100, the control system 1 may be configured such that the DSMcontroller 105 is omitted to directly input the reference input Rsld_ffor the cam phase control to the variable cam phase mechanism 70 as thephase control input Ucain. Furthermore, the control system 1 may beconfigured such that when the lift control input Uliftin is calculatedin the valve lift controller 110, the DSM controller 115 is omitted todirectly input the reference input Rsld_f′ for the valve lift control tothe variable valve lift mechanism 50 as the lift control input Uliftin.Similarly, the control system 1 may be configured such that also whenthe compression ratio control input Ucr is calculated in the compressionratio controller 120, the DSM controller 125 is omitted to directlyinput the reference input Rsld_f″ for the compression ratio control tothe variable compression ratio mechanism 80 as the compression ratiocontrol input Ucr.

Further, in the compensation element 100, in the calculation of thedisturbance compensation value Rcyc_lin, the count C_crk of the crankangle counter may be replaced by the count of a counter incremented byan amount corresponding to a predetermined cam angle in synchronism withgeneration of each pulse of the CAM signal, and the valve lift Liftin bythe target valve lift Liftin_cmd. Further, in the compensation elements110 and 120 as well, the disturbance compensation values Rcyc_lin andRcyc_cr may be calculated in the same manner.

Further, when the engine 3 is not provided with the variable valve liftmechanism 50 and the variable cam phase mechanism 70, but is providedwith the variable compression ratio mechanism 80 alone, the compensationelement 120 may calculated the disturbance compensation value Rcyc_craccording to a parameter (intake pipe absolute pressure and the THpassing intake air amount GTH) indicative of load on the engine 3 inplace of the cam phase Cain and the valve lift Liftin.

Still further, although in the first embodiment, the cam phase Cain andthe valve lift Liftin are used as load parameters, this is notlimitative, but any load parameters may be employed so long as they areindicative of the load on the engine 3. For example, the target camphase Cain_cmd and the target valve lift Liftin_cmd may be used as theload parameters or the intake pipe absolute pressure PBA, the TH passingintake air amount GTH, and the accelerator pedal opening AP may also beused.

Further, in place of the hydraulic variable cam phase mechanism 70 ofthe control system according to the present embodiment, anelectromagnetic variable cam phase mechanism that the present assigneehas already proposed in Japanese Patent Application No. 2003-293009 maybe employed as the variable cam phase mechanism. In this case, in theelectromagnetic variable cam phase mechanism, since the cam phase Cainis changed depending on the balance between the electromagnetic force ofa solenoid and the urging force of a spring, the periodic disturbanceacts only on the advanced side or the retarded side. Therefore, tocompensate for the periodic disturbance acting as above, when thedisturbance compensation value Rcyc_cin for the cam phase control iscalculated, the map value Rcyc_bs cin thereof may be calculated using amap indicated by solid lines or broken lines in FIG. 37.

Next, a description will be given of a control system 1A according to asecond embodiment of the present invention. The control system 1A of thepresent embodiment is configured similarly to the above-describedcontrol system 1 of the first embodiment, except for part thereof.Therefore, the following description will be mainly given of thedifferent points thereof from the control system 1 of the firstembodiment. Referring to FIG. 38 to FIG. 40, the control system 1Aincludes a cam phase controller 200, a valve lift controller 210, and acompression ratio controller 220, all of which are implemented by theECU 2 (disturbance estimation value-calculating means).

First, a description will be given of the cam phase controller 200.Referring to FIG. 38, the cam phase controller 200 includes a target camphase-calculating section 201 (target cam phase-setting means, targetvalue-setting means), a compensation element 202 (disturbancecompensation value-storing means, disturbance compensationvalue-selecting means), a two-degree-of-freedom SLD controller 203(control input-calculating means), a DSM controller 205 (controlinput-calculating means), and an adaptive disturbance observer 206(disturbance estimation value-calculating means), all of which areimplemented by the ECU 2. In the cam phase controller 200, the targetcam phase-calculating section 201 and the compensation element 202 areconstructed similarly to those of the cam phase controller 100,described hereinabove, and hence detailed description thereof isomitted.

The adaptive disturbance observer 206 is provided for calculating adisturbance estimation value c1 for the cam phase control, which is usedfor compensating for modeling errors and disturbance. More specifically,in the adaptive disturbance observer 206, the disturbance estimationvalue c1 for the cam phase control is calculated with an identificationalgorithm of a fixed gain method, expressed by equations (17) to (19) inFIG. 41, according to the cam phase Cain, the disturbance compensationvalue Rcyc_cin for the cam phase control, and the SLD control input Rsldfor the cam phase control. Cain_hat in the equation (17) represents anidentified value of the cam phase, and e_id in the equation (18) anidentification error. Further, P′ in the equation (19) represents anidentification gain.

It should be noted that the above equations (17) to (19) are derived asfollows: When the disturbance estimation value c1 and the disturbancecompensation value Rcyc_cin both for the cam phase control are added tothe aforementioned model expressed by the equation (9) in FIG. 20 so asto compensate for disturbance, an equation (20) shown in FIG. 41 isobtained. In the equation (20), a right side thereof is substituted withthe identified value Cain_hat of the cam phase, and by using a modelobtained by the substitution and the identification algorithm of thefixed gain method based on a statistical process, such that thedifference between the identified value Cain_hat of the cam phase andthe cam phase Cain is minimized, the above described equations (17) to(19) are derived.

In the adaptive disturbance observer 206, with the algorithm expressedby the equations (17) to (19), the disturbance estimation value c1 forthe cam phase control is calculated as a value capable of suitablycompensating for modeling errors and disturbance.

Further, in the two-degree-of-freedom SLD controller 203, the SLDcontrol input Rsld (control input) for the cam phase control iscalculated with a target value filter-type two-degree-of-freedom slidingmode control algorithm expressed by equations (21) to (27) in FIG. 42.As is clear from the equations (21) to (27), the control algorithm forthe two-degree-of-freedom SLD controller 203 is different from thecontrol algorithm for the two-degree-of-freedom SLD controller 103 inthat the disturbance compensation value Rcyc_cin and the disturbanceestimation value c1 for the cam phase control are contained in theequation for calculating the equivalent control input Req, and theadaptive law input Radp is not used in calculation of the SLD controlinput Rsld.

Further, in the DSM controller 205, the phase control input Ucain iscalculated based on the SLD control input Rsld for the cam phasecontrol, calculated as above, with a control algorithm [equations (28)to (33) shown in FIG. 43] similar to the control algorithm for the DSMcontroller 105.

The cam phase controller 200 is configured as described above, and thevalve lift controller 210 is also configured similarly to the cam phasecontroller 200. More specifically, as shown in FIG. 39, the valve liftcontroller 210 includes a target valve lift-calculating section 211(target value-setting means, target valve lift-setting means), acompensation element 212 (disturbance compensation value-storing means,disturbance compensation value-selecting means), a two-degree-of-freedomSLD controller 213 (control input-calculating means), a DSM controller215 (control input-calculating means), and an adaptive disturbanceobserver 216 (disturbance estimation value-calculating means). In thevalve lift controller 210, the target valve lift-calculating section 211and the compensation element 212 are configured similarly to those ofthe above-described valve lift controller 110, and hence detaileddescription thereof is omitted.

In the adaptive disturbance observer 216, a disturbance estimation valuec1′ for the valve lift control is calculated with an algorithm similarto the algorithm for the adaptive disturbance observer 206 of the camphase controller 200. More specifically, the disturbance estimationvalue c1′ for the valve lift control is calculated with an algorithm inwhich in the above equations (17) to (19) in FIG. 41, Cain is replacedby Liftin, Cain_cmd by Liftin_cmd, Rcyc_cin by Rcyc_lin, c1 by c1′, andRsld by Rsld′, respectively, and the coefficients and the like arereplaced by respective corresponding values for the valve lift control.

Further, in the two-degree-of-freedom SLD controller 213, the SLDcontrol input Rsld′ for the valve lift control is calculated with analgorithm similar to the algorithm for the two-degree-of-freedom SLDcontroller 203 of the cam phase controller 200. More specifically, theSLD control input Rsld′ (control input) for the valve lift control iscalculated with an algorithm in which in the equations (21) to (27) inFIG. 42, the parameters, the coefficients and the like are replaced byrespective corresponding values for the valve lift control.

Further, in the DSM controller 215, the lift control input Uliftin iscalculated based on the SLD control input Rsld′ for the valve liftcontrol, calculated as above, with a control algorithm similar to thecontrol algorithm for the DSM controller 205 of the cam phase controller200. More specifically, the lift control input Uliftin is calculatedwith an algorithm in which in the equations (28) to (33) in FIG. 43, theparameters, the coefficients and the like are replaced by respectivecorresponding values for the valve lift control.

On the other hand, the compression ratio controller 220 as well isconstructed similarly to the cam phase controller 200. Morespecifically, as shown in FIG. 40, the compression ratio controller 220includes a target compression ratio-calculating section 221 (targetvalue-setting means, target compression ratio-setting means), acompensation element 222 (disturbance compensation value-storing means,disturbance compensation value-selecting means), a two-degree-of-freedomSLD controller 223 (control input-calculating means), a DSM controller225 (control input-calculating means), and an adaptive disturbanceobserver 226 (disturbance estimation value-calculating means). In thecompression ratio controller 220, the target compressionratio-calculating section 221 and the compensation element 222 areconfigured similarly to those of the above-described compression ratiocontroller 120, and hence detailed description thereof is omitted.

Further, in the adaptive disturbance observer 226, a disturbanceestimation value c1″ for the compression ratio control is calculatedwith an algorithm similar to the algorithm for the adaptive disturbanceobserver 206 of the cam phase controller 200. More specifically, thedisturbance estimation value c″ for the compression ratio control iscalculated with an algorithm in which in the above equations (17) to(19) in FIG. 41, Cain is replaced by Cr, Cain_cmd by Cr_cmd, Rcyc_cin byRcyc_cr, c1 by c1″, and Rsld by Rsld″, and the coefficients and the likeare replaced by respective corresponding values for the compressionratio control.

Further, in the two-degree-of-freedom SLD controller 223, the SLDcontrol input Rsld″ (control input) for the compression ratio control iscalculated with an algorithm similar to the algorithm for thetwo-degree-of-freedom SLD controller 203 of the cam phase controller200. More specifically, the SLD control input Rsld″ for the compressionratio control is calculated with an algorithm in which in the equations(21) to (27) in FIG. 42, the parameters, the coefficients and the likeare replaced by respective corresponding values for the valve liftcontrol.

Further, in the DSM controller 225, the compression ratio control inputUcr is calculated based on the SLD control input Rsld″ for thecompression ratio control, calculated as above, with a control algorithmsimilar to the control algorithm for the DSM controller 205 of the camphase controller 200. More specifically, the compression ratio controlinput Ucr is calculated with an algorithm in which in the equations (28)to (33) in FIG. 43, the parameters, the coefficients and the like arereplaced by respective corresponding values for the compression ratiocontrol.

In the control system 1A, when the phase control inputs Ucain, Uliftin,and Ucr are calculated by the ECU 2, the phase control input Ucain iscalculated by the equations (21) to (33) in the aforementioned step 26in FIG. 32. Further, in the step 27, the lift control input Uliftin iscalculated with the algorithm in which the variables and the parametersin the equations (21) to (33) are replaced by the respectivecorresponding values for the valve lift control, and in the step 28, thecompression ratio control input Ucr is calculated by the same method.

According to the control system 1A of the present embodiment, configuredas above, similarly to the control system 1 of the first embodiment, thethree control inputs Ucain, Uliftin, and Ucr are calculated according tothe three disturbance compensation values Rcyc_cin, Rcyc_lin, andRcyc_cr, respectively. Therefore, by controlling the cam phase Cain, thevalve lift Liftin, and the compression ratio Cr in a feedforward mannerusing the control inputs Ucain, Uliftin, and Ucr calculated as above,respectively, it is possible to quickly compensate for and suppress theinfluence of the periodic disturbance on the cam phase Cain, the valvelift Liftin, and the compression ratio Cr. As a result, in the cam phasecontrol, the valve lift control, and the compression ratio control, itis possible to obtain the same advantageous effects as provided by thecontrol system 1 described hereinabove.

Moreover, the disturbance estimation values c1, c1′, and c1″ arecalculated as values capable of compensating for modeling errors anddisturbance, by the adaptive disturbance observers 206, 216, and 226,and the control inputs Ucain, Uliftin, and Ucr are calculated accordingto the disturbance estimation values c1, c1′, and c1″. Therefore, byusing the control inputs Ucain, Uliftin, and Ucr, it is possible tocontrol the cam phase Cain, the valve lift Liftin, and the compressionratio Cr, such that a steady-state deviation is prevented fromoccurring, and compensate for and suppress the influence of the periodicdisturbance on the cam phase Cain, the valve lift Liftin, and thecompression ratio Cr, more quickly than the control system 1 accordingto the first embodiment. Thus, it is possible to further enhance thestability and the accuracy of the control compared with the controlsystem 1.

Next, a description will be given of a control system 1B according to athird embodiment of the present invention. The control system 1B of thepresent embodiment is configured similarly to the above-describedcontrol system 1A of the second embodiment, except for part thereof.Therefore, the following description will be mainly given of thedifferent points thereof from the control system 1A of the secondembodiment. Referring to FIGS. 44 to 46, the control system 1B includesa cam phase controller 300, a valve lift controller 310, and acompression ratio controller 320, all of which are implemented by theECU 2 (model parameter-identifying means).

First, a description will be given of the cam phase controller 300.Referring to FIG. 44, the cam phase controller 300 includes a target camphase-calculating section 301 (target value-calculating means, targetcam phase-setting means), a compensation element 302 (disturbancecompensation value-storing means, disturbance compensationvalue-selecting means), a two-degree-of-freedom SLD controller 303(control input-calculating means), a DSM controller 305 (controlinput-calculating means), and a partial parameter identifier 307(amplitude correction value-calculating means, modelparameter-identifying means). The cam phase controller 300 isdistinguished from the above-described cam phase controller 200 in thatit has the partial parameter identifier 307 in place of theabove-described disturbance observers 206, and accordingly part of acontrol algorithm for the two-degree-of-freedom SLD controller 303 isdifferent from the control algorithm for the two-degree-of-freedom SLDcontroller 203.

In the partial parameter identifier 307, a parameter vector θ isidentified with a sequential identification algorithm of the fixed gainmethod, expressed by equations (34) to (39) in FIG. 47, according to thecam phase Cain, the disturbance compensation value Rcyc_cin for the camphase control, and the SLD control input Rsld for the cam phase control.The transposed matrix of the parameter vector θ is expressed by theequation (38). In the equation (38), d1 represents a disturbancecompensation value gain as an amplitude correction value, and isprovided for compensating for a change in the amplitude of the periodicdisturbance, caused by the aging of the variable cam phase mechanism 70and a variation between individual mechanisms 70. Further, in theequation (34), W represents an imaginary output, and in the equation(35), W_hat represents an identified value of the imaginary output.Further, in the equation (37), e_id′ represents an identification errordefined by the equation (36), P″ a predetermined identification gain,and ζ a vector whose transposed matrix is expressed by the equation(39).

It should be noted that the above equations (34) to (39) are derived asfollows: When the disturbance compensation value gain d1 is added to themodel expressed by the equation (20) in FIG. 41, an equation (40) shownin FIG. 47 is obtained. In the equation (40), if each variable isshifted by an amount corresponding to one discrete time period,parameters b1 and b2, the disturbance compensation value gain d1, andthe disturbance compensation value Rcyc_cin are discretized, and theterm of Cain is moved to the left side of the equation (40), then anequation (41) in FIG. 47 is obtained. In the equation (41), if the leftside thereof is defined as W, and the right side thereof as W_hat, thenthe above equations (34) and (35) are obtained. Here, it is possible toconsider W as the output of an imaginary controlled object, W_hat as anidentified value of the output of the imaginary controlled object, andthe equation (35) as a model of the imaginary controlled object.Therefore, by using the sequential identification algorithm of the fixedgain method so as to identify the model parameters of the imaginarycontrolled object such that the imaginary output W is made closer to theidentified value W_hat of the imaginary output, the above equations (34)to (39) are derived.

In the partial parameter identifier 307, the model parameters b1 and b2,the disturbance estimation value c1, and the disturbance compensationvalue gain d1 are sequentially identified with the identificationalgorithm expressed by the equations (34) to (39).

Further, in the two-degree-of-freedom SLD controller 303, the SLDcontrol input Rsld for the cam phase control is calculated with a targetvalue filter-type two-degree-of-freedom sliding mode control algorithmexpressed by equations (42) to (48) in FIG. 48. As is clear from thereference to the equations (42) to (48), the control algorithm for thetwo-degree-of-freedom SLD controller 303 is different from the controlalgorithm for the two-degree-of-freedom SLD controller 203 only in thatin the calculation of the equivalent control input Req, the disturbancecompensation value Rcyc_cin for the cam phase control is multiplied bythe disturbance compensation value gain d1.

Further, in the DSM controller 305, the phase control input Ucain iscalculated based on the SLD control input Rsld for the cam phasecontrol, calculated as above, with a control algorithm [equations (49)to (54) shown in FIG. 49] similar to the control algorithm for the DSMcontroller 205.

Next, a description will be given of the valve lift controller 310. Thevalve lift controller 310 as well is configured similarly to the camphase controller 300. More specifically, as shown in FIG. 45, the valvelift controller 310 includes a target valve lift-calculating section 311(target value-setting means, target valve lift-setting means), acompensation element 312 (disturbance compensation value-storing means,disturbance compensation value-selecting means), a two-degree-of-freedomSLD controller 313 (control input-calculating means), a DSM controller315 (control input-calculating means), and a partial parameteridentifier 317 (model parameter-identifying means, amplitude correctionvalue-calculating means). The valve lift controller 310 is distinguishedfrom the aforementioned valve lift controller 210 in that it has thepartial parameter identifier 317 in place of the above-mentioneddisturbance observer 216, and accordingly part of a control algorithmfor the two-degree-of-freedom SLD controller 313 is different from thecontrol algorithm for the two-degree-of-freedom SLD controller 203.

In the partial parameter identifier 317, model parameters b1′ and b2′, adisturbance estimation value c1′, and a disturbance compensation valuegain d1′ (amplitude correction value), for the valve lift control, aresequentially identified with an algorithm similar to the algorithm forthe partial parameter identifier 307 of the cam phase controller 300.More specifically, the model parameters b1′ and b2′, the disturbanceestimation value c1′, and the disturbance compensation value gain d1′,for the valve lift control, are sequentially identified with analgorithm in which in the equations (34) to (39) shown in FIG. 47, b1,b2, c1, and d1 are replaced by b1′, b2′, c1′, and d1′, respectively, andCain by Liftin, Rcyc_cin by Rcyc_lin, and Rsld by Rsld′, and further thecoefficients and the like being replaced by respective correspondingvalues for the valve lift control.

Further, in the two-degree-of-freedom SLD controller 313, the SLDcontrol input Rsld′ for the valve lift control is calculated with analgorithm similar to the algorithm for the two-degree-of-freedom SLDcontroller 303 of the cam phase controller 300. More specifically, theSLD control input Rsld′ for the valve lift control is calculated with analgorithm in which in the equations (42) to (48) in FIG. 48, theparameters, the coefficients and the like are replaced by respectivecorresponding values for the valve lift control.

Furthermore, in the DSM controller 315, the lift control input Uliftinis calculated based on the SLD control input Rsld′ for the valve liftcontrol, calculated as above, with a control algorithm similar to thecontrol algorithm for the DSM controller 305 of the cam phase controller300. More specifically, the lift control input Uliftin is calculatedwith an algorithm in which in the equations (49) to (54) in FIG. 49, theparameters, the coefficients and the like are replaced by respectivecorresponding values for the valve lift control.

On the other hand, the compression ratio controller 320 as well isconfigured similarly to the cam phase controller 300. More specifically,as shown in FIG. 46, the compression ratio controller 320 includes atarget compression ratio-calculating section 321 (target value-settingmeans, target compression ratio-setting means), a compensation element322 (disturbance compensation value-storing means, disturbancecompensation value-selecting means), a two-degree-of-freedom SLDcontroller 323 (control input-calculating means), a DSM controller 325(control input-calculating means), and a partial parameter identifier327 (model parameter-identifying means, amplitude correctionvalue-calculating means).

In the partial parameter identifier 327, model parameters b1″ and b2″, adisturbance estimation value c1″, and a disturbance compensation valuegain d1″ (amplitude correction value), for the compression ratiocontrol, are sequentially identified with an algorithm similar to thealgorithm for the partial parameter identifier 307 of the cam phasecontroller 300. More specifically, the model parameters b1″ and b2″, thedisturbance estimation value c1″, and the disturbance compensation valuegain d1″, for the compression ratio control, are sequentially identifiedwith an algorithm in which in the equations (34) to (39) shown in FIG.47, b1, b2, c1, and d1 are replaced by b1″, b2″, c1″, and d1″,respectively, and Cain by Cr, Rcyc_cin by Rcyc_cr, and Rsld by Rsld″,and further the coefficients and the like by respective correspondingvalues for the compression ratio control.

Further, in the two-degree-of-freedom SLD controller 323, the SLDcontrol input Rsld″ for the compression ratio control is calculated withan algorithm similar to the algorithm for the two-degree-of-freedom SLDcontroller 303 of the cam phase controller 300. More specifically, theSLD control input Rsld″ for the compression ratio control is calculatedwith an algorithm in which in the equations (42) to (48) in FIG. 48, theparameters, the coefficients and the like are replaced by respectivecorresponding values for the compression ratio control.

Furthermore, in the DSM controller 325, the compression ratio controlinput Ucr is calculated based on the SLD control input Rsld″ for thecompression ratio control, calculated as above, with a control algorithmsimilar to the control algorithm for the DSM controller 305 of the camphase controller 300. More specifically, the compression ratio controlinput Ucr is calculated with an algorithm in which in the equations (49)to (54) in FIG. 49, the parameters, the coefficients and the like arereplaced by respective corresponding values for the compression ratiocontrol.

According to the control system 1B of the present embodiment, configuredas above, similarly to the control systems 1 and 1A of the first andsecond embodiments, the three control inputs Ucain, Uliftin, and Ucr arecalculated according to the three disturbance compensation valuesRcyc_cin, Rcyc_lin, and Rcyc_cr, respectively. Therefore, by controllingthe cam phase Cain, the valve lift Liftin, and the compression ratio Crin a feedforward manner using the control inputs Ucain, Uliftin, and Ucrcalculated as above, respectively, it is possible to quickly compensatefor and suppress the influence of the periodic disturbance on the camphase Cain, the valve lift Liftin, and the compression ratio Cr. As aresult, in the cam phase control, the valve lift control, and thecompression ratio control, it is possible to obtain the sameadvantageous effects as provided by the above-described control system1.

Further, in the cam phase controller 300 of the control system 1B, themodel parameters b1 and b2, the disturbance estimation value c1, and thedisturbance compensation value gain d1 are sequentially identified, andthe SLD control input Rsld for the cam phase control is calculated bythe two-degree-of-freedom SLD controller 303, according to the valuesb1, b2, c1, and d1, identified as above, and the disturbancecompensation value Rcyc_cin for the cam phase control. Then, the phasecontrol input Ucain is calculated based on the SLD control input Rsldfor the cam phase control. Therefore, even when the amplitude of theperiodic disturbance is changed due to the aging of the variable camphase mechanism 70, and a variation between individual mechanisms 70,the phase control input Ucain makes it possible to cause the cam phaseCain to converge to the target cam phase Cain_cmd quickly andaccurately, while properly compensating for the change in the amplitudeof the periodic disturbance. That is, the cam phase controller 300 iscapable of compensating for and suppress the influence of the periodicdisturbance on the cam phase Cain more quickly than the cam phasecontroller 200 according to the second embodiment. As described above,it is possible to further enhance the stability and the accuracy of thecam phase control compared with the cam phase controller 200 accordingto the second embodiment.

Moreover, the valve lift controller 310 and the compression ratiocontroller 320 make it possible to obtain the same advantageous effectsas provided by the cam phase controller 300, whereby it possible tofurther enhance the stability and the accuracy of the valve lift controland the compression ratio control compared with the valve liftcontroller 210 and the compression ratio controller 220 according to thesecond embodiment.

Although the cam phase controller 300 according to the presentembodiment is configured such that part of the model parameters (b1,b2), the disturbance estimation value c1, and the disturbancecompensation value gain d1 are identified by the partial parameteridentifier 307, this is not limitative, but a parameter identifier foridentifying all the model parameters a1, a2, b1, and b2, the disturbanceestimation value c1, and the disturbance compensation value gain d1 maybe employed in place of the partial parameter identifier 307, or anidentifier for identifying only the disturbance compensation value gaind1 may be employed in place of the partial parameter identifier.

Further, although in the partial parameter identifier 307, theidentification algorithm of the fixed gain method is used, anotheridentification algorithm than this may be used. For example, a variablegain method, a δ correcting method or a σ correcting method, each ofwhich is an improved algorithm of the fixed gain method, anidentification algorithm in which a model parameter scheduler and the δcorrecting method are combined may be employed. Further, it goes withoutsaying that also in the controllers 310 and 320, the partial parameteridentifiers 317 and 327 may be configured as above.

Although in the above-described embodiments, the control systemaccording to the present invention is applied to the control of a systemincluding the variable cam phase mechanism 70, the variable valve liftmechanism 50, and the variable compression ratio mechanism 80, ascontrolled objects (moving part-driving mechanisms), this is notlimitative, but it is to be understood that the control system accordingto the present invention can be applied to control of movingpart-driving mechanisms for various kinds of industrial machines, towhich the periodic disturbance is applied.

Further, although in the above embodiments, the variable cam phasemechanism 70 is configured to change the phase Cain of the intakecamshaft 5 with respect to the crankshaft 3 d, this is not limitative,but the variable cam phase mechanism may be configured to change thephase of the exhaust camshaft 8 with respect to the crankshaft 3 d.Further, it may be configured to change the phases of both of the intakecamshaft 5 and the exhaust camshaft 8 with respect to the crankshaft 3d. When the variable cam phase mechanism is thus configured to becontrolled with the above-described control algorithms, it is possiblenot only to obtain the advantageous effects described above but also toquickly compensate for and suppress the influence of the periodicdisturbance on an exhaust valve system. This makes it possible to avoidreduction of the internal EGR amount due to the influence of theperiodic disturbance to thereby ensure a stable combustion state.

Furthermore, although in the above-described embodiments, the variablevalve lift mechanism 50 is configured to change the lift Liftin of theintake valves 4, this is not limitative, but the variable valve liftmechanism may be configured to change the lift of the exhaust valves 7.Further, it may be configured to change the lifts of both of the intakevalves 4 and the exhaust valves 7. When the variable valve liftmechanism is thus configured to be controlled with the aforementionedcontrol algorithms, it is possible not only to obtain the advantageouseffects described above but also to quickly compensate for and suppressthe influence of the periodic disturbance on the exhaust valve system.This makes it possible to avoid a change in the internal EGR amount dueto the influence of the periodic disturbance to thereby ensure a stablecombustion state.

It is further understood by those skilled in the art that the foregoingis a preferred embodiment of the invention, and that various changes andmodifications may be made without departing from the spirit and scopethereof.

1. A control system for controlling an output of a controlled object towhich is applied a periodic disturbance an amplitude of whichperiodically changes, by a control input, comprising: disturbancecompensation value-storing means for storing a plurality of disturbancecompensation values for compensating for the periodic disturbance, thedisturbance compensation values having been set in advance in timeseries according to a result of prediction of a change in the amplitudeof the periodic disturbance; disturbance compensation value-selectingmeans for selecting, in timing of selection at a repetition periodcorresponding to 1/n (n is an integer not smaller than 2) of arepetition period of occurrence of the periodic disturbance, onedisturbance compensation value corresponding to the timing of selection,from the stored disturbance compensation values; and controlinput-calculating means for calculating the control input, with apredetermined control algorithm, according to the selected disturbancecompensation value.
 2. A control system for controlling an output of acontrolled object to which is applied a periodic disturbance anamplitude of which periodically changes, by a control input, comprising:disturbance compensation value-storing means for storing a plurality ofdisturbance compensation values for compensating for the periodicdisturbance, the disturbance compensation values having been set inadvance in time series according to a result of prediction of a changein the amplitude of the periodic disturbance; disturbance compensationvalue-selecting means for selecting, in timing of selection at arepetition period corresponding to 1/n (n is an integer not smaller than2) of a repetition period of occurrence of the periodic disturbance, onedisturbance compensation value corresponding to the timing of selection,from the stored disturbance compensation values; disturbance estimationvalue-calculating means for calculating a disturbance estimation valuefor compensating for a disturbance and modeling errors in the controlledobject, with a predetermined estimation algorithm based on a modeldefining relationships between the disturbance estimation value, thecontrol input, and the output of the controlled object; and controlinput-calculating means for calculating the control input, with apredetermined control algorithm, according to the selected disturbancecompensation value.
 3. A control system for controlling an output of acontrolled object to which is applied a periodic disturbance anamplitude of which periodically changes, by a control input, comprising:disturbance compensation value-storing means for storing a plurality ofdisturbance compensation values for compensating for the periodicdisturbance, the disturbance compensation values having been set inadvance in time series according to a result of prediction of a changein the amplitude of the periodic disturbance; disturbance compensationvalue-selecting means for selecting, in timing of selection at arepetition period corresponding to 1/n (n is an integer not smaller than2) of a repetition period of occurrence of the periodic disturbance, onedisturbance compensation value corresponding to the timing of selection,from the stored disturbance compensation values; modelparameter-identifying means for identifying model parameters of a modeldefining relationships between the disturbance compensation value, thecontrol input, and the output of the controlled object, with apredetermined identification algorithm; and control input-calculatingmeans for calculating the control input, with a predetermined algorithmincluding a predetermined control algorithm based on the model,according to the identified model parameters and the selecteddisturbance compensation value.
 4. A control system for controlling anoutput of a controlled object to which is applied a periodic disturbancean amplitude of which periodically changes, by a control input,comprising: disturbance compensation value-storing means for storing aplurality of disturbance compensation values for compensating for theperiodic disturbance, the disturbance compensation values having beenset in advance in time series according to a result of prediction of achange in the amplitude of the periodic disturbance; disturbancecompensation value-selecting means for selecting, in timing of selectionat a repetition period corresponding to 1/n (n is an integer not smallerthan 2) of a repetition period of occurrence of the periodicdisturbance, one disturbance compensation value corresponding to thetiming of selection, from the stored disturbance compensation values;amplitude correction value-calculating means for calculating anamplitude correction value for correcting an amplitude of thedisturbance compensation value, with a predetermined algorithm based ona model defining relationships between the amplitude correction value,the disturbance compensation value, the control input, and the output ofthe controlled object; and control input-calculating means forcalculating the control input, with a predetermined control algorithm,according to the calculated amplitude correction value and the selecteddisturbance compensation value.
 5. A control system as claimed in anyone of claims 1 to 4, further comprising target value-setting means forsetting a target value of the output of the controlled object, andwherein the predetermined control algorithm includes aresponse-specifying control algorithm for causing the output of thecontrolled object to converge to the target value.
 6. A control systemas claimed in any one of claims 1 to 4, further comprising targetvalue-setting means for setting a target value of the output of thecontrolled object, and wherein the predetermined control algorithmincludes a two-degree-of-freedom control algorithm for causing theoutput of the controlled object to converge to the target value.
 7. Acontrol system as claimed in any one of claims 1 to 4, wherein thecontrolled object includes a variable cam phase mechanism for changing acam phase, the cam phase being defined as at least one of a phase of anintake camshaft and a phase of an exhaust camshaft of an internalcombustion engine with respect to a crankshaft, and wherein the outputof the controlled object is the cam phase changed by the variable camphase mechanism, and wherein the control input is inputted to thevariable cam phase mechanism.
 8. A control system as claimed in any oneof claims 1 to 4, wherein the controlled object includes a variablevalve lift mechanism for changing a valve lift, the valve lift beingdefined as at least one of a lift of intake valves and a lift of exhaustvalves of an internal combustion engine, and wherein the output of thecontrolled object is the valve lift changed by the variable valve liftmechanism, and wherein the control input is inputted to the variablevalve lift mechanism.
 9. A control system as claimed in any one ofclaims 1 to 4, wherein the controlled object includes a variablecompression ratio mechanism for changing a compression ratio of aninternal combustion engine, wherein the output of the controlled objectis the compression ratio changed by the variable compression ratiomechanism, and wherein the control input is inputted to the variablecompression ratio mechanism.
 10. A control system for a movingpart-driving mechanism which changes at least one of operation timingand an operation amount of a moving part of an internal combustionengine, and to which is applied a periodic disturbance an amplitude ofwhich periodically changes along with rotation of a crankshaft of theengine, comprising: disturbance compensation value-storing means forstoring a plurality of disturbance compensation values for compensatingfor the periodic disturbance, the disturbance compensation values havingbeen set in advance according to a result of prediction of a change inamplitude of the periodic disturbance caused by the rotation of thecrankshaft; disturbance compensation value-selecting means forselecting, in timing of selection corresponding to each rotation of thecrankshaft of the engine through a predetermined angle, a disturbancecompensation value corresponding to the timing of selection from thestored disturbance compensation values; and control input-calculatingmeans for calculating a control input for control of the movingpart-driving mechanism, with a predetermined control algorithm,according to the selected disturbance compensation value.
 11. A controlsystem as claimed in claim 10, wherein the moving part-driving mechanismincludes a variable cam phase mechanism for changing a cam phase as theoperation timing of the moving part, the camp phase being defined as atleast one of a phase of an intake camshaft and a phase of an exhaustcamshaft of the engine with respect to the crankshaft.
 12. A controlsystem as claimed in claim 11, wherein said disturbance compensationvalue-selecting means selects the disturbance compensation value furtheraccording to a cam phase parameter indicative of the cam phase.
 13. Acontrol system as claimed in claim 11, wherein the engine includes avariable valve lift mechanism for changing a valve lift, the valve liftbeing defined as at least one of a lift of intake valves and a lift ofexhaust valves of the engine, and wherein the disturbance compensationvalues are set further according to results of prediction of at leastone of the change in the amplitude and a change in a behavior of theperiodic disturbance, caused by a change in the valve lift by thevariable valve lift mechanism, and wherein said disturbance compensationvalue-selecting means selects the disturbance compensation value furtheraccording to a valve lift parameter indicative of the valve lift.
 14. Acontrol system as claimed in claim 11, wherein said controlinput-calculating means corrects the disturbance compensation valueaccording to a rotational speed of the engine, and calculates thecontrol input according to the corrected disturbance compensation value.15. A control system as claimed in claim 11, wherein said controlinput-calculating means calculates the control input irrespective of thedisturbance compensation value, when the rotational speed of the engineis not lower than a predetermined rotational speed.
 16. A control systemas claimed in claim 11, further comprising target cam phase-settingmeans for setting a target cam phase as a target of the cam phase, andwherein the predetermined control algorithm includes a predeterminedresponse-specifying control algorithm for causing the cam phase toconverge to the target cam phase.
 17. A control system as claimed inclaim 11, further comprising disturbance estimation value-calculatingmeans for calculating a disturbance estimation value for compensatingfor a disturbance and modeling errors in the variable cam phasemechanism, with a predetermined estimation algorithm based on a modeldefining relationships between the disturbance estimation value, thecontrol input, and the cam phase, and wherein said controlinput-calculating means calculates the control input further accordingto the calculated disturbance estimation value.
 18. A control system asclaimed in claim 11, further comprising model parameter-identifyingmeans for identifying model parameters of a model defining relationshipsbetween the disturbance compensation value, the control input, and thecam phase, with a predetermined identification algorithm, and whereinsaid control input-calculating means calculates the control input withthe predetermined control algorithm including a predetermined algorithmformed based on the model, according to the identified model parameters.19. A control system as claimed in claim 10, wherein the movingpart-driving mechanism includes a variable valve lift mechanism forchanging a valve lift as the operation amount of the moving part, thevalve lift being defined as at least one of a lift of intake valves anda lift of exhaust valves of the engine.
 20. A control system as claimedin claim 19, wherein said disturbance compensation value-selecting meansselects the disturbance compensation value further according to a valvelift parameter indicative of the valve lift.
 21. A control system asclaimed in claim 19, wherein the engine includes a variable cam phasemechanism for changing a cam phase, the cam phase being defined as atleast one of a phase of an intake camshaft and a phase of an exhaustcamshaft of the engine with respect to the crankshaft, and wherein saiddisturbance compensation value-selecting means selects the disturbancecompensation value further according to a cam phase parameter indicativeof the cam phase.
 22. A control system as claimed in claim 19, whereinsaid control input-calculating means corrects the disturbancecompensation value according to a rotational speed of the engine, andcalculates the control input according to the corrected disturbancecompensation value.
 23. A control system as claimed in claim 19, whereinsaid control input-calculating means calculates the control inputirrespective of the disturbance compensation value, when the rotationalspeed of the engine is not lower than a predetermined rotational speed.24. A control system as claimed in claim 19, further comprising targetvalve lift-setting means for setting a target valve lift as a target ofthe valve lift, and wherein the predetermined control algorithm includesa predetermined response-specifying control algorithm for causing thevalve lift to converge to the target valve lift.
 25. A control system asclaimed in claim 19, further comprising disturbance estimationvalue-calculating means for calculating a disturbance estimation valuefor compensating for a disturbance and modeling errors in the variablevalve lift mechanism, with a predetermined estimation algorithm based ona model defining relationships between the disturbance estimation value,the control input, and the valve lift, and wherein said controlinput-calculating means calculates the control input further accordingto the calculated disturbance estimation value.
 26. A control system asclaimed in claim 19, further comprising model parameter-identifyingmeans for identifying model parameters of a model defining relationshipsbetween the disturbance compensation value, the control input, and thevalve lift, with a predetermined identification algorithm, and whereinsaid control input-calculating means calculates the control input withthe predetermined control algorithm including a predetermined algorithmformed based on the model, according to the identified model parameters.27. A control system as claimed in claim 10, wherein the movingpart-driving mechanism includes a variable compression ratio mechanismfor changing a compression ratio of the engine by changing a stroke ofpistons of the engine as the operation amount of the moving part.
 28. Acontrol system as claimed in claim 27, wherein said disturbancecompensation value-selecting means selects the disturbance compensationvalue further according to a compression ratio parameter indicative ofthe compression ratio.
 29. A control system as claimed in claim 27,wherein said control input-calculating means corrects the disturbancecompensation value according to a rotational speed of the engine, andcalculates the control input according to the corrected disturbancecompensation value.
 30. A control system as claimed in claim 27, whereinsaid control input-calculating means corrects the disturbancecompensation value according to a load parameter indicative of load onthe engine, and calculates the control input according to the correcteddisturbance compensation value.
 31. A control system as claimed in claim30, wherein the engine includes a variable cam phase mechanism forchanging a cam phase, the cam phase being defined as at least one of aphase of an intake camshaft and a phase of an exhaust camshaft of theengine with respect to the crankshaft, and wherein the load parameterinclude a cam phase parameter indicative of the cam phase.
 32. A controlsystem as claimed in claim 30, wherein the engine includes a variablevalve lift mechanism for changing a valve lift, the valve lift beingdefined as at least one of a lift of intake valves and a lift of exhaustvalves of the engine, and wherein the load parameter include a valvelift parameter indicative of the valve lift.
 33. A control system asclaimed in claim 29, wherein said control input-calculating meanscalculates the control input irrespective of the disturbancecompensation value, when the rotational speed of the engine is not lowerthan a predetermined rotational speed.
 34. A control system as claimedin claim 27, further comprising target compression ratio-setting meansfor setting a target compression ratio as a target of the compressionratio, and wherein the predetermined control algorithm includes apredetermined response-specifying control algorithm for causing thecompression ratio to converge to the target compression ratio.
 35. Acontrol system as claimed in claim 27, further comprising disturbanceestimation value-calculating means for calculating a disturbanceestimation value for compensating for a disturbance and modeling errorsin the variable compression ratio mechanism, with a predeterminedestimation algorithm based on a model defining relationships between thedisturbance estimation value, the control input, and the compressionratio, and wherein said control input-calculating means calculates thecontrol input further according to the calculated disturbance estimationvalue.
 36. A control system as claimed in claim 27, further comprisingmodel parameter-identifying means for identifying model parameters of amodel defining relationships between the disturbance compensation value,the control input, and the compression ratio, with a predeterminedidentification algorithm, and wherein said control input-calculatingmeans calculates the control input with the predetermined controlalgorithm including the predetermined algorithm based on the model,according to the identified model parameters.